Regeneration

Regeneration was the process of "molecular readjustment" (PROSE: ) by which Time Lords and others renewed themselves, causing a complete physical and often psychological change. It could happen because of severe illness, (TV: , , , ; AUDIO: ) old age, fatigue, (TV: , , ) or injury. (TV: , , , , , , , , , , , PROSE: ) It could also be invoked by choice, whether voluntary (TV: , , , ) or involuntary. (TV: , COMIC: )
Conversely, regeneration could be prevented by choice, although choosing not to regenerate from fatal damage was essentially an act of suicide. (TV: ) However, a Time Lord could delay the actual change in appearance and enter "a state of grace" for a brief period of time. (TV: , , ) Precise damage to a Time Lord could also cause a delay in the regeneration starting. (TV: , ,)
There was a general lack of consensus upon whether regeneration was a natural process which all Gallifreyans possessed, (PROSE: ) a natural process which the Time Lords developed through exposure to the Time Vortex (TV: ) or the Eye of Harmony, (PROSE: ) or if it was a manufactured process, created through experimentation, and possibly by being stolen from other beings predating the Time Lords. (TV: , PROSE: )
Regeneration was described by the scientist Davros as "the ancient magic of the Time Lords", (TV: ) and was also described as "witchcraft" by the Sycorax. (TV: )
== Background ==
=== Origins ===
Many different explanations were given for the origins of regeneration, although most agreed that regenerations typically came in cycles of twelve. Some of these accounts suggested that regeneration originated on Gallifrey, either occurring naturally (TV: , PROSE: ) or through experimentation. (AUDIO: ; PROSE: , ) Other accounts suggested that regeneration was an ability with non-Gallifreyan origins, which the Time Lords took for themselves through experimentation. (TV: , PROSE: )
==== Naturally occurring ====
Some accounts suggested that regeneration was a natural process found on Gallifrey. One of these accounts, which the Eleventh Doctor explained to Vastra, stated that exposure over billions of years to the Untempered Schism contributed to the Time Lords' ability to regenerate. This was also what allowed for River Song's regenerative abilities, as she was conceived in the Doctor's TARDIS whilst it traversed the Time Vortex (TV: ) and was then conditioned into a proto-Time Lord by the Kovarian Chapter. (AUDIO: )
Another account found in historian Postar the Perfidious's Scrolls of Gallifrey stated that Rassilon was the first Time Lord to gain regeneration as an unintended side-effect of his work with the Eye of Harmony. Due to the elemental forces which he had been exposed to as he worked on stabilising the Eye, his original body died and underwent the first ever regeneration. Rassilon gained a set of twelve regenerations as a result, and upon reshaping Time Lord society to his designs, Rassilon then gave a select number of Gallifreyan aristocrats the privilege of gazing upon the Eye unveiled, thus granting each of them twelve regenerations as well. Morbius would later partially base his campaign for the Presidency on the promise of extending the same generosity to all Gallifreyans. (PROSE: )
A distinctly different account by one Gallifreyan suggested, however, that regeneration was a process innate to all Gallifreyans, and was not exclusive to the Time Lords. (PROSE: ) Gallifreyans could in fact regenerate into new bodies before they had even established themselves as the Lords of Time, with Omega regenerating into a muscular form sometime before the creation of the Hand of Omega. (PROSE: )
==== Artificially created ====
Some accounts suggested that regeneration originated on Gallifrey, but came about as a result of experimentation. Several of these accounts involved the experiments of Rassilon. Indeed, by the time of Rassilon's ill-fated intervention on Kolstan, Artron, his contemporary, knew that Rassilon had "experimented" with a limited sort of regeneration. (AUDIO: ) A limit of twelve regenerations ultimately became standard among Time Lords, with additional regeneration cycles being granted to certain Time Lords only under exceptional circumstances. (TV: , AUDIO: ) Among the reasons given for the limited cycles were that the mind could not handle the multiplicity of psyches, (PROSE: ) and that Rassilon ultimately came to consider total immortality a curse. (TV: )
One of these accounts held that Cardinal Rassilon had been investigating a method of regenerating decayed and diseased tissue via a series of self-replicating, biogenic molecules. The cells of a Gallifreyan body would be repaired, restored and reorganised, resulting in a wholly new physical form. The brain cells would also be rearranged, though to a lesser extent; the new incarnation would retain the memories of the former incarnation, though the personality of the Time Lord could change. The degree in which the personality changed during regeneration varied between Time Lords and even between incarnations. Rassilon intended for regeneration to be reserved for only the Gallifreyan elite. According to this account, another reason that Rassilon imposed a limit of twelve regenerations was to avoid decaying biogenic molecules. (AUDIO: )
Another account suggested that regeneration was the result of Time Lords having triple-helix DNA. The third strand of DNA was added by Rassilon, which enabled regeneration. (PROSE: )
According to several accounts, however, Rassilon was not responsible for the creation of regeneration. One of these accounts, given by the Black Scrolls of Rassilon, indicated that regeneration was instead caused by a virus created by Thremix, (PROSE: ) which ravaged ancient Gallifreyan society when Rassilon seized power. (PROSE: , )
Another account suggested that the ability to regenerate was only present in Loom-born Gallifreyans, being a product of the Looming process. This account indicates that earlier womb-born generations of Gallifreyans could not regenerate. (PROSE: )
==== Stolen from other species ====
Some accounts suggested that regeneration did not originate on Gallifrey, but was rather stolen from species that predated the Time Lords through experimentation. One of these accounts, described by to the Thirteenth Doctor, suggested that regeneration on Gallifrey began with the Timeless Child, who Tecteun, a Shobogan explorer and scientist, had discovered on another planet, adopted, and then brought home. The child proved capable of regenerating their body an indefinite number of times, being of another species from an unknown realm. The First Tecteun began experimenting upon her child, and eventually unravelled the mystery of regeneration by discovering the regeneration code. She put this to the test on her own biology, and regenerated into a new male incarnation. The Second Tecteun gave the gift of regeneration to all other Gallifreyans within the Citadel, and would go on to found Time Lord society alongside the other Founding Fathers of Gallifrey. He also limited the number of regenerations each Time Lord got to twelve. The Timeless Child went on to become the Doctor, but eventually had their memories erased following their service as an agent of the Division. The Doctor was transformed back into a child and grew up again with no recollection of their former life, as well as a limited regeneration cycle. All records in the Matrix with explicit information on the Timeless Child and the origins of regeneration were redacted as the Founding Fathers wanted a "noble creation myth" instead. (TV: ) What little remained was disguised with a visual filter that instead depicted the story of Brendan, an immortal Irish policeman. (TV: ) The Thirteenth Doctor accepted this account, but later claimed the limited number of regenerations was a limit in the power of regeneration itself that the Shobogans discovered instead of creating. (PROSE: )
Another account suggested by Richard Francis Burton, upon observing the similarities between Time Lord regeneration and the rapid healing of the Mal'akh, theorised that early Time Lords obtained regenerative abilities by knowingly infecting themselves with the Yssgaroth taint. (PROSE: ) Indeed, the Great Vampires were searching for a "Child-That-Was-Taken". (PROSE: )
=== The workings of regeneration ===
Time Lords released massive amounts of a hormone called lindos in moments of extreme trauma, and it was this hormone which triggered regeneration. Newly regenerated Time Lords could be identified by elevated levels of lindos in their system. (PROSE: , AUDIO: )
Time Lords were also said to have "packets" of regeneration energy in their bodies, one for each life. These packets could be physically removed from a Time Lord's body, essentially robbing them of their regenerations. (TV: )
During regeneration, a Time Lord experienced a surge of pure regenerative energy, as their entire system was rewritten and their universe moulded into a new shape, with their very biodata being rewritten in the fabric of space-time. (PROSE: ) Unfortunately, their immune systems were seriously weakened as the process took place, with the result that they could be infected by viruses such as the Faction Paradox biodata virus that would normally have had no effect on them. (PROSE: ) On a wider scale, regenerations were so important to a Time Lord's timeline that even minor temporal paradoxes during the process of regeneration could have devastating consequences. (AUDIO: , TV: )
The Fourth Doctor explained that he still had the same body as his first incarnation; it had just been restructured a lot since then. He agreed that the process of regeneration went against Newton's Third Law, and added that he did violate a few laws "now and then". (PROSE: )
The Thirteenth Doctor described regenerating from her previous incarnation as "every cell in [her] body burning" as her "whole body changed". She stated that, while changing, "there's this moment when you're sure you're about to die and then... you're born." She deemed the process as "terrifying". (TV: )
The Fourteenth Doctor described how allowing a regeneration to begin was like sneezing after holding it in for "too long." (PROSE: )
=== Process ===
==== Appearance ====
During a regeneration, a Time Lord's body could shine with milky white light, (TV: ; PROSE: ) a swirl of rainbow colours (TV: , , ) or no colours, (COMIC: ) crackle with electricity, (TV: ) appear to be engulfed in flames, (PROSE: Exodus, COMIC: ) or discharge golden energy, which could vary in speed and intensity from being brief and contained to explosive and capable, in extreme circumstances, of causing damage to the nearby area. (COMIC: , , TV: , , , , , , , , , , , , , , , , , PROSE: )
In other cases, there was no apparent energy discharge at all, just a fade away to the next incarnation. (TV: , PROSE: , ) In the case of the Doctor's fourth regeneration, the Doctor appeared to merge with and become the Watcher, after which he transformed from the Watcher into his fifth incarnation. (TV: ) On the occasion that the Doctor had just been granted a brand new regeneration cycle, he initially emitted a large eruption of energy in an almost liquid form. Sometime later, when his actual shift to a new body occurred, there was only a very short, almost negligible discharge of energy. (TV: ) When mortally wounded by the Toymaker, the Fourteenth Doctor's body momentarily glowed with regeneration energy before dissipating. (TV: )
Some regenerations occurred with other individuals in close proximity. These times, the energy from the Doctor's body wasn't particularly violent. (TV: , , , , , ) However, from their eighth incarnation onward, the Doctor warned anyone in close proximity to a regeneration to keep away. This happened with members of the Sisterhood of Karn prior to the Eighth Doctor transforming into his so-called War Doctor incarnation, (TV: ) when the Ninth Doctor received a brief surge of regenerative energy in the presence of Rose Tyler, (TV: ) and when the Eleventh Doctor realised that Mels was regenerating. (TV: ) When the Tenth Doctor regenerated during the 2009 Dalek invasion of Earth, Captain Jack Harkness similarly warned Rose Tyler to stay away from the Doctor when his regeneration started. (TV: ) Why the Doctor thought this was necessary became clear when the Tenth Doctor's regeneration into the Eleventh caused enough damage to the TARDIS to force a complete reconstruction into a different design. (TV: )
Indeed, the Doctor came to realise that his regenerations were growing more explosive; (PROSE: ) when he began his thirteenth regeneration, it was the most destructive of all — emitting a shock-wave resembling a thermonuclear blast. The town of Christmas was levelled, Dalek fighter pods were blown out of the sky, and the Dalek flagship (TV: ) and Dalek fleet were destroyed. (PROSE: ) Because the Doctor didn't have time to warn the citizens of Christmas of the danger from regenerating, his companion Clara Oswald ushered the people into the bell tower to take shelter. The Daleks that remained on the street were blown to pieces. (TV: ) The Twelfth Doctor was able to tell that his fourteenth regeneration would be explosive, (PROSE: ) and it eventually caused enough damage to the TARDIS for it to malfunction. The control room exploded, sending the Thirteenth Doctor plummeting from its doors. (TV: )
However, when the Fourteenth Doctor expected to regenerate, he accepted the company of Donna Noble and Melanie Bush as they each took one of his hands, assisting his bi-generation from the Fifteenth Doctor. (TV: )
==== Physical and mental change ====
During regeneration, there were the genetic equivalents of "bit errors" in the DNA of the regenerating cells. The Time Lord would change in appearance, height, mass or apparent age. The personality would also change; even the cells and chemistry of the brain regenerated, although their blood type would remain the same in all their lives. (PROSE: ) Allergies and dominant limbs could also change between regenerations. (AUDIO: ) According to the Sixth Doctor, a Time Lord's basic personality traits remained unchanged throughout all their lives, but the balance of said traits could be affected by regeneration. (AUDIO: ) With each incarnation, the Doctor's memory worked differently, (PROSE: ) with some of their memories from before regeneration being lost even after the new incarnation had mentally stabilised, unless they were specifically reminded of relevant events. (TV: , , )
When he fell unconscious after being exposed to radiation, the Sixth Doctor heard the voice of his successor before the regeneration began in full, leaving him assured that he would regenerate despite the circumstances of his death, the voices of the two Doctors briefly merging in his mind as they each noted that their life was far from over. (AUDIO: ) When the Eighth Doctor was stabbed by Charley while he was possessed by anti-time, he nearly died permanently due to his current grief, but found himself conversing with the personas of his immediate three predecessors who helped him realise what had happened and the need to return to life to stop Rassilon controlling the power of anti-time. (AUDIO: ) Indeed, the metaphysical Edge of Existence was a location in the Doctor's mind where each incarnation passed during regeneration, entering the Doctor's subconscious as a new persona emerged.
After a forced regeneration into , the Thirteenth Doctor found herself at the Edge but refused to pass, meeting past incarnations who acted as the Guardians of the Edge. (TV: ) When the amnesiac Eighth Doctor was in a coma after his chest was crushed by sandbags, during his coma fantasy he experienced a feeling that he compared to the idea of his body as a coat that he could take off and don another body around a corner, but in this instance the Doctor did not need to regenerate as his current link to Sabbath would sustain his life even after such serious injuries. (PROSE: )
On rare instances, regeneration could change a Time Lord's clothing, as happened when the First Doctor became the Second Doctor, (TV: , ) and when the Thirteenth Doctor became the Fourteenth Doctor, the latter acknowledging his resemblance to a previous incarnation. (TV: , PROSE: ) Most other cases would have the regenerated Time Lord in the attire of their predecessor. (TV: , etc.) The Fourteenth Doctor's bi-generation split his outfit evenly on himself and the Fifteenth Doctor. (TV: )
While most regenerations caused Time Lord's to take on an entirely new appearance, it seemed that in very rare circumstances they could regenerate into previous appearances. The Thirteenth Doctor's regeneration caused the Fourteenth Doctor to look identical to a previous incarnation, even down to the teeth, something that shocked the newly regenerated Doctor. In addition, this regeneration changed the Doctor's clothing. (TV: ) Donna Noble suggested that this was because the regeneration was influenced by the Doctor's subconscious desire to settle down with a family - specifically, the Noble family. (TV: ) The Curator had previously noted to the Eleventh Doctor that they may find themselves revisiting a few old faces in years to come with the Curator himself having the appearance of an elderly Fourth Doctor. (TV: )
Generally, most newly regenerated Time Lords appeared physically younger than their preceding incarnations, (TV: , , ) so much so that the First Doctor assumed it to be the natural result of regeneration. (TV: ) Indeed, the Tenth Doctor once told Rose Tyler that regeneration was an alternative to ageing. (TV: ) However, this was not always the case; the "dashing young" Eleventh Doctor was dismayed to find that he would become the "old" Twelfth Doctor, with his companion Clara Oswald remarking that the new Doctor did not look "renewed". (TV: ) However, the Eleventh Doctor had aged considerably, to the point that he was on the brink of dying of old age, when he was enabled to regenerate, though he was able to briefly "reset" to his youthful appearance before the change of appearance. (TV: ) Following her second regeneration, River Song, formerly Mels Zucker, observed herself to have a "mature" appearance. (TV: )
Ohila offered the Eighth Doctor the choice of whether his successor would be "young or old"; (TV: ) before that, the Second Doctor rejected two potential faces offered to him by the Time Lords, one "too old" and another "too young". (TV: ) According to the Valeyard, there was also a risk of emerging from a regeneration as a Time Tot rather than an adult Time Lord. (AUDIO: ) River Song's second incarnation started off as a baby, (TV: , ) while Rassilon actually had the opposite happen to him, changing from the body of a middle-aged man to that of an elderly man. (TV: ) One of the Master's Time War incarnations resembled a small male child, only for it to be undone into his more elderly War incarnation. (COMIC: , )
Despite the apparent changes in physical age, observers such as River Song, Clara Oswald and Cindy Wu found that they could identify younger incarnations of the Doctor by looking into their eyes. (TV: , , COMIC: )
One source stated that Time Lords were born with just one heart and grew a second heart on regeneration. This included the Doctor, who in their first incarnation had only one heart. (PROSE: ) Other accounts showed Time Lords having two hearts in their original incarnation, such as the Doctor (AUDIO: , ) and Jenny. (TV: ) Tegan Jovanka was under the belief that the second heart of a Time Lord was only developed upon the first regeneration, much to the surprise of Leela, who believed that a Time Lord always had two hearts, with neither being sure who was correct. (AUDIO: ) Regeneration also changed the location of said hearts. (TV: , , )
According to the Eleventh Doctor, every regeneration was painful, (TV: ) with the Seventh Doctor once describing regeneration as a good and bad feeling in the same way driving a car very fast was a good and bad feeling, enjoying the exhilaration of the process but knowing you were going to "die" at the end. (PROSE: ) Klyst assured Louis following his first regeneration that the first was always more painful than subsequent ones. (AUDIO: )
Regeneration could also change a Time Lord's biological sex. The Doctor, the Master, the Monk, Drax, Rindle, and Lake each had female incarnations, while the majority of their incarnations were male. (TV: , , AUDIO: , , ) The General was usually a woman, but one of their incarnations was a bald white male. (TV: ) Other Time Lords changed sex more evenly; a male incarnation of Volstrom regenerated to female form, then back to male, and then female again. (AUDIO: ) Missy (TV: ) and the Thirteenth Doctor (TV: ) referred to their regenerations to female form as an "upgrade", a term also used by River Song when discussing the former's change. (AUDIO: )
Skin colour could also change between regenerations. (TV: , , PROSE: , AUDIO: , ) Though fluctuations in gender, size and skin colour appeared to be fairly common, the Twelfth Doctor stated that he was "one of those stuck-in-a-rut Time Lords who always [had] the same model of body." (PROSE: )
More extreme physical changes were also possible. Cavis regenerated a complete body after being decapitated, although the process was cut short when she was stabbed through both hearts (the one that she already possessed and the one that she was growing as she regenerated), and her lover Gandar became a kind of human-Silurian hybrid in appearance when he regenerated in the realm of Avalon mere hours after his previous change. (PROSE: )
When the Eleventh Doctor lost his leg during the Siege of Trenzalore, he grew a new one after his body was "reset" as his new regeneration cycle began. The Twelfth Doctor had both legs once he had regenerated. (TV: , )
In the early days of regeneration, it was possible for fragments of other DNA to be incorporated into the new incarnation if, for example, a Time Lord had recently eaten or spent a great deal of time around other species; the early Gallifreyan priest I.M. Foreman suffered from this problem throughout his regenerations, each incarnation becoming more and more inhuman as more foreign DNA was incorporated into the process. (PROSE: , )
As well as the obvious benefits of purging Time Lords of any poisons or diseases that might have caused their deaths, regeneration could have more subtle benefits. As each Time Lord accumulated artron energy throughout their lives, regeneration reset the artron energy levels in their bodies to a pre-set level to prevent it rising to a point where the radiation could threaten them. (PROSE: ) When the Sirens of Time attempted to make the Doctor their agent, while responding to the Sirens' call more than once would have brought the Doctor permanently under their control, the Doctor was still a free agent as he had responded to their call three times in three different incarnations, suggesting that regeneration would purge the Sirens' influence. (AUDIO: )
However, this purge would not include assets, as the Seventh Doctor retained an immunity to the Swarm virus despite receiving that immunity in his fourth incarnation. (AUDIO: ) Some negative influences could not be purged by regeneration; while the Fourth Doctor was able to resist succumbing to the breath of forever, (AUDIO: ) he was still susceptible to the influence of the Eminence in his sixth incarnation. (AUDIO: )
==== Non-humanoid forms ====
Although Time Lords usually favoured humanoid forms in regeneration, this was not universal. One Time Lord, Lord Cardinal Zero, regenerated into an avian lifeform as a result of the poison which triggered the regenerative process. (AUDIO: ) When Romana regenerated from her first to second incarnation, the Fourth Doctor advised her not to "wear" Princess Astra's body and to "try another" body. Before once again assuming Astra's form, she tried various others, including a short blue humanoid and an extremely tall woman. (TV: ) although according to another source, this particular episode was just the TARDIS matrix playing a trick on the Doctor. (PROSE: ) In another instance, the Archon Lotto had a fourth body resembling that of a dog, and a fifth had that of an anthropomorphic lioness. Though Lotto was originally a biological human despite his ability to change body, rather than a native of the Archon's Homeworld. (PROSE: )
Although all of the Doctor's known bodies could pass for human but for minor internal differences, their eleventh incarnation stated clearly that he could become "anything", (TV: ) and the Ninth Doctor once suggested that two heads or even no head were both possible. (TV: ) Shortly after regenerating, the Eleventh Doctor had even made it a priority — even amidst serious damage to his TARDIS — to immediately conduct a physical inventory to make sure he still had two legs, both hearts and sufficient fingers, eyes, ears, a nose, chin and hair. (TV: ) The Tenth Doctor, upon meeting a Skithra Queen inside a future Doctor's TARDIS control room, briefly wondered if she was the future incarnation of himself that he had run into, although he was soon proven wrong. (COMIC: ) Novice Hame once claimed that among the Doctor's many faces and forms were those of animals, although she also claimed many of said forms were other individuals who take his title. (WC: )
During the War in Heaven, regeneration into extremely non-humanoid bodies became the norm for members of the House Military, although bodies without obvious facial features were considered "informal"; this was the case even for a strategist like Entarodora. However, the same tendencies were implemented in the regen-inf soldiers, members of the lesser species who had been granted regeneration to serve as disposable foot-soldiers for the Great Houses, who often resented having no choice but to transform into gigantic, living weapons upon death. (PROSE: ) At least one Homeworlder soldier in the House Military, who fought in the Battle of Cratosi Fields, shared this mindset; upon beginning to regenerate from a humanoid form into a monstrous form with razor-sharp mandibles where her throat should have been, she broke down sobbing, begging all who would hear her to help her not to change. (PROSE: )
==== After-effects ====
thumb|The Fifth Doctor experiences post-regeneration trauma. (TV: )
Regeneration mixed up the synapses in the brain, sometimes resulting in negative after effects. (AUDIO: ) During the first few hours of the regeneration, the Time Lord could suffer from confusion, erratic behaviour, extended periods of unconsciousness, or memory loss. (TV: , , , , , AUDIO: , et al.) Motor control could be impaired; the Eleventh Doctor expressed difficulty "steering" his new body, having walked into a tree minutes earlier, and a Time Lord could suffer random spasms as the regeneration settled. (TV: ) The Tenth Doctor noted "energy deficiency" was common after regenerating, which could lead to an increase in appetite to supplement the energy loss. (TV: )
The Thirteenth Doctor explained a Time Lord had new instincts upon regenerating; they must trust these instincts to shape their personality. Until then, the Time Lord had no clue what kind of person they had become. (TV: ) The Tenth Doctor stated that he would have no clue what kind of person he would become until he experienced new things. (TV: ) However, it was possible for Time Lords to retain a quirk or choice throughout their lives, such as the Doctor's promise (TV: ) and the Corsair's tattoo. (TV: )
The Doctor, in particular, seemed to be highly susceptible to post-regenerative side-effects. After their first regeneration, the Second Doctor had some confusion over his own identity, although he adjusted to his new body reasonably quickly. (TV: ) The Doctor's third incarnation was incapacitated for some time after a forced regeneration by the Time Lords. (TV: ) Likewise, their fourth incarnation suffered acute delirium and memory loss and was placed under bed rest for a few days until he regained consciousness. (TV: ) It took a while for the newly regenerated Fifth Doctor to remember his own identity, experiencing fainting spells and sudden spurts of alternating energy and fatigue until he stabilised. (TV: ) Their sixth incarnation confused myths with reality, resulting in him trying to strangle Peri before coming to his senses, and experienced erratic mood swings of enthusiasm or depression until he became reasonably stable. (TV: ) The Seventh Doctor was sufficiently weakened that was able to effectively brainwash him. (TV: ) The Eighth Doctor suffered from amnesia and emotional instability, after having been declared dead for some time prior to regenerating due to the anaesthetic that had been used on his previous body. (TV: ) The War Doctor showed no after-effects after regeneration, (TV: ) as Ohila's elixir assisted in the process. (PROSE: 
The Ninth Doctor mentioned being "not quite calibrated" after regeneration, and likened himself to a soft shell crab waiting to harden, (PROSE: ) and the newly regenerated Tenth Doctor spent hours unconscious after an initial burst of wild enthusiasm. (TV: ) Immediately post-regeneration, the Eleventh Doctor craved various foods, which he hated upon tasting them. (TV: ) At the start of a new regeneration cycle, the Twelfth Doctor experienced severe memory loss, forgetting how to pilot the TARDIS, (TV: ) and spent the next few hours in a delirious state. He was unable to remember names and distinguish people from each other, to the point that he confused Clara Oswald with both Handles and Strax. (TV: ) The Thirteenth Doctor began her life with some amnesia, unable to remember her own name. However, most of her memories and all of her intellect remained intact. Like the Tenth Doctor, she passed out and slept for a long period of time to recover, expelling regeneration energy while she was asleep. Though she was also awoken early due to circumstances, she did not suffer serious health complications like the Tenth Doctor did. She later regained access to her memories after an adrenalin rush from confronting Tzim-Sha. (TV: ) Curiously, the Fourteenth Doctor did not experience any of the usual post-regeneration side-effects, (COMIC: ) although the Doctor did question his appearance. (PROSE: ), TV: )
On two occasions, the Doctor crashed the TARDIS following regeneration, first when the Tenth Doctor compulsively sped up the TARDIS and hit it against a wall in the Powell Estate, (TV: , ) and again when the Tenth Doctor's regeneration into the Eleventh damaged the TARDIS, causing it to crash land into a garden shed in Leadworth. (TV: , ) The Thirteenth Doctor was thrown out of her TARDIS after damage dealt by her regeneration caused an explosive malfunction. (TV: )
As regeneration involved completely rewriting a Time Lord's biodata and exposing it to the Time Vortex, for a time, the Eighth Doctor speculated that his raw biodata was responsible for the transformation of his companion Sam Jones from her original dark-haired, self-destructive self into his blonde-haired "perfect" companion, as his biodata was particularly exposed after his traumatic regeneration and the opening of the Eye of Harmony. However, Professor Daniel Joyce dismissed this theory for blonde Sam's existence as impossible as the Doctor could never have had that degree of unintentional influence on a complete stranger, although he admitted that the basic concept of Time Lord biodata rewriting another person's biodata wasn't completely impossible if there was greater pre-existing contact between them. (PROSE: )
A Zero Room could help with the regeneration-recovery process, as it removed all outside distractions. (TV: ) After his first regeneration, the Second Doctor implied that the TARDIS itself helped the process along. (TV: ) The Second Doctor helped a dying Pavo to regenerate by bringing the other Time Lord into his TARDIS. (AUDIO: ) The Eighth Doctor offered to take Sandun into his TARDIS, as well, to help with the latter's first regeneration. (AUDIO: ) After regenerating, the Tenth Doctor said he needed the TARDIS. In some cases proper rest helped a Time Lord's mind heal, but waking too soon prolonged the need of it; it was referred to as a "neural implosion". He later explained that some tannin in tea helped heal the synapses, accelerating the healing process. (TV: )
Were a Time Lord knocked unconscious, the whole process might start all over again. (PROSE: ) Indeed, the Fourth Doctor thought that he had regenerated again without noticing when the Brigadier told him he had "changed" (referring to his clothes, not his appearance). (TV: ) However, this was not a certainty, (TV: ) as it seemed that sleep would help a Time Lord recover from post-regenerative delirium. (TV: , , , , )
After a while, the Time Lord's body would settle down, though they could regrow lost limbs within the first fifteen hours of the regeneration due to residual energy. (TV: , ) The residual energy also provided a Time Lord with significantly greater endurance; the Twelfth Doctor fell out of a tree but remained unaffected by it. (TV: ) The Thirteenth Doctor fell out of the stratosphere and into a train without suffering any major damage, even reacting as if she had fallen from a simple loss of balance. (TV: ) Melody Pond, following her second and final regeneration, not only used her regenerative energy to survive a hail of gunfire by Nazi soldiers but channelled it into a focused blast of energy that knocked out the entire squad. (TV: )
Even after the physical transformation, changes could occur. The Doctor was excessively tired after their third regeneration, falling asleep in many odd locations. (TV: ) The Fifth Doctor's hair went from longer to shorter to longer in the space of a few days. (PROSE: ) For a short time after regenerating, a Time Lord displayed greater strength than usual; the Doctor's fourth incarnation was able to karate-chop a brick in half shortly after his regeneration, though he failed to repeat the action once fully recovered, (TV: ) while their eighth incarnation broke down a steel door with his bare foot immediately following his regeneration. (TV: )
Forced regenerations could also result in Time Lords losing some of their skills or memories in various incarnations. Some of these changes could be minor, such as the Fourth Doctor reflecting that he was no longer able to make successful soufflés, (PROSE: ) while on two occasions, later Doctors were forced to mentally regress back to their third persona, when they found themselves facing a situation where the Third Doctor's skills would be better-suited to handle the crisis than their own abilities were. This happened during their sixth and seventh incarnations. The Sixth Doctor required the Third's skills at hand-to-hand combat (PROSE: ) while the Seventh felt that his technical expertise would be useful. (PROSE: ) The Fifth Doctor also notably lacked the hand-to-hand combat skills of his two immediate predecessors, though he remained a fairly capable swordsman, (TV: ) and the Twelfth Doctor expressed uncertainty about his ability to use a motorbike early in his life as he hadn't had a chance to test his current capabilities. (PROSE: ) Post-regenerative amnesia could also be a problem, preventing the Doctors' recall of crucial information, such as the Sixth Doctor forgetting about his predecessor's encounter with Katherine Chambers when he met a younger version of her despite his past self's attempt to leave a reminder, resulting in him being unable to avert Katherine's interest in acquiring Cyber-technology. (AUDIO: , )
Personal tastes could also vary between different incarnations, such as the Fifth Doctor not being a particularly strong drinker, (AUDIO: ) while the Fourth (TV: ) and Sixth (PROSE: ) enjoyed the chance to get drunk, the Fourth Doctor expressing surprise at the attire he would wear in his sixth (AUDIO: ) and eleventh bodies (PROSE: ) when he caught glimpses of his future, or the Eleventh Doctor enjoying football, (TV: ) while the Twelfth considered it a boring sport. (TV: )
The mental transformation caused by regeneration could also be a problem; when Andred decided to pose as Torvald after the two fought in the Capitol basement, Torvald dying while Andred regenerated, immediate post-regenerative trauma was so difficult that Andred didn't think about what his actions would do to his wife Leela before he was too far into his deception, (AUDIO: ) others noting later that Andred had spent so long pretending to be Torvald that his own new personality had never asserted itself, resulting in him still expressing some of Torvald's personality traits even after his deception was exposed. (AUDIO: )
However, some Time Lords were able to regenerate with little or no overt complications, as in the case of Romana (TV: ) and River Song, (TV: ) neither of whom appeared to experience any sign of incapacitation in their exploits immediately following regeneration. Both treated the change rather casually and acted as normal. (TV: , ) The General showed no after-effects after regenerating into her twelfth incarnation, in fact stating that she was "back to normal". (TV: )
==== Long term after-effects ====
The Doctor was sometimes unsure what adventure happened within what regeneration. (AUDIO: ) However, the Doctor's memories and the Doctor's time stream were subject to great deals of change and flux. (AUDIO: ; PROSE: )
The Fourth Doctor tended to get a minor headache whenever he remembered something that happened to him in a previous regeneration. (PROSE: )
=== Limitations ===
River Song and the Silence believed that a Time Lord could die permanently if killed "again" at the right time during the regenerative process. This appeared to be verified when River, controlled by the Silence, seemingly managed to kill the Eleventh Doctor permanently after he began to regenerate at Lake Silencio, (TV: ) although unbeknownst to the Silence, the Doctor she shot was actually a simulacrum, the Teselecta, used by the Doctor to fake his death (TV: ) and was already out of regenerations. (TV: ) Indeed, the Tenth Doctor told Wilfred Mott that he could still be killed before regeneration kicked in. (TV: )
Though Time Lords could regenerate after severe injuries, regeneration was by no means guaranteed. Artron energy was crucial to the regenerative process, meaning Time Lords were unable to regenerate if they did not have any artron energy in their body. (PROSE: , AUDIO: ) The regenerative process could also be destroyed by acid (PROSE: ) or by exposures to substances, such as anaesthetics meant for humans, which were toxic to the Gallifreyan body. (TV: )
Certain energy weapons could also prevent the regenerative process. In an alternate reality, a Raxacoricofallapatorian used an energy weapon that destroyed the Tenth Doctor's regenerative process, preventing his regeneration into the Eleventh Doctor. (COMIC: ) A planet of executioners possessed a machine built for executing Time Lords that could disable regeneration as part of the execution process. (TV: ) Martha Jones also had a gun that, when inserted with four distinct chemicals, could apparently prevent regeneration, as she reportedly planned to do to . While the existence of this gun was actually a ruse created by the Tenth Doctor to distract the Master from their real plan, the fact that the Master believed it suggests that such a weapon was theoretically possible. (TV: ) According to some accounts, a blast from staser fire could prevent regeneration. Maxil implied this, (TV: ) and Gandar later explicitly noted that a staser pistol was one of the few weapons capable of killing a Time Lord immediately. (PROSE: ) However, the Twelfth Doctor shot the Eleventh General once with the sidearm of the President's personal security, triggering the General's regeneration. (TV: ) Several Time Lords died without regenerating when they were killed by a TCE. (TV: )
When the Tenth Doctor tried to attach his brain to the CAL Data Core, believing he could regenerate and provide the extra memory space, River pointed out it would outright kill him by burning out both of his hearts, so she took his place. (TV: ) The Master's upgraded laser screwdriver could disable the regenerative process if its target received a full blast on its maximum setting. (TV: ) While not explicitly demonstrated, the Master at least believed that Janis thorns could prevent regeneration, as he went to great lengths to brainwash Leela so that she would use the thorns against the Fourth Doctor, the Doctor only surviving this experience as he was able to help Leela break the Master's programming in time for her to inject him with the antidote. (AUDIO: )
Certain injuries only had a chance of causing regeneration if left untreated; when the Doctor was paralysed from the waist down after a spaceship crash, he expressed concern that he would regenerate if he passed out while being transported, but he made it back to the TARDIS without regenerating and was able to find healing nanites that could repair his back. (AUDIO: )
Some injuries were so serious that they could not be treated by regeneration; when the Time Lady Solenti was blinded, she spent ninety-one years uncertain if she would ever regain her sight, although a telepathic exchange with a pan-dimensional race allowed her to confirm that the neural pathways for sight in her brain were still intact and she would be able to see again once she regenerated, even if she decided that she would not regenerate just to regain her vision. (PROSE: )
According to some accounts, the regenerative process could only kick in when the body was still alive to some extent; as a result, final deaths could occur too quickly for the body to regenerate, as evidenced by how an alternate version of the Tenth Doctor died because he was drowned confronting the Empress of the Racnoss. (TV: ) When facing the Word Lord, the Seventh Doctor sacrificed himself to stop Nobody No-One by using a tablet linked to the Trans-Galactic net to hit Nobody with the full force of the stories collected about himself, at the cost of frying his own mind, causing so much damage that he expressed a belief that this would kill him even before the Word Lord tricked a UNIT soldier into declaring "Nobody can stop the Doctor from regenerating" which gave the Word Lord the power to do just that. Fortunately, this sacrifice was undone when the Seventh Doctor's future self - currently present at the death of his past self after his own attempt to trap the Word Lord - set up a complex plan that allowed Ace to subvert the Word Lord's power to rewrite reality so that she could undo the Doctor's death, restoring him to life in his seventh body with no need for regeneration. (AUDIO: ) However, in other accounts, regeneration could occur even after the previous incarnation's body had completely died, or indeed, been dead for some time — although this could result in some "growing pains" for the new incarnation, who might deal with such conditions as amnesia. (TV: )
By some accounts, stabbing or shooting a Time Lord through both hearts at the same time would kill them. (PROSE: , ) , having already gravely wounded the Eighth Doctor by shooting him in one of his hearts, threatened to take out the other if he attempted to regenerate. (AUDIO: ) Missy recommended eight snipers, with two trained on each of her hearts and three for her brain stem, so that Clara Oswald could feel safe while speaking to her, noting that they'd have to "switch [her] off fast" before she could regenerate. (TV: ) Plans to execute a Time Lord relied on technology that would destroy both hearts, sever all three brain stems, and deliver a cellular shock to prevent regeneration, after which the subject would be left in a quantum vault for no less than a thousand years to ensure that regeneration would not occur. (TV: )
Time Lords could also be injured beyond the point of regeneration, with copies of the Twelfth Doctor dying after contact with the Veil inside his confession dial. In such cases, the Doctor claimed that every cell in a Time Lord's body would continue attempting to regenerate, which could prolong their actual death for several days. In his case, this gave each copy time to use the last of their energy to trigger a teleportation device and "create" a new body for their essence to continue trying to escape. (TV: )
It was suggested that regeneration may not occur if the Time Lord lacked the will for it to do so. Indeed, refused to regenerate upon being shot by Lucy Saxon, instead deciding to die in the Tenth Doctor's arms to mock his rival. (TV: ) An alternate version of the Sixth Doctor was killed permanently by a Dalek, but this Doctor had been locked away in the Tower of London for decades after his legs had been amputated, and his mental state had significantly deteriorated, to the point that he may have wanted to die to escape his nightmarish existence. (AUDIO: ) The Doctor's Cousin Arkhew was unable to regenerate after being strangled by Owis, but Arkhew was noted as being a very weak-willed Time Lord who feared how he was perceived by others. (PROSE: )
When the Eighth Doctor was infected by anti-time and asked his companion Charley to kill him, while talking with his predecessors in his mind, he speculated that he was not regenerating because he had wanted to die out of grief and Charley's new hatred of what he had become, requiring support from his predecessors to allow the anti-time to take him over and let Zagreus defeat Rassilon. (AUDIO: )
The Eighth Doctor was killed when the ship he was trying to escape from crash landed on Karn. He was later restored temporarily to life by the Sisterhood of Karn and provided with an elixir to trigger the regenerative process. (TV: ) The Ninth Doctor showed the same level of concern as his human companions did towards falling victim to the Gelth, suggesting regenerating was not an expected outcome. (TV: ) When surrounded by Daleks, the Doctor was under the belief that he would die for good, remarking that "maybe it's time". (TV: )
Certain environments could also be dangerous for regeneration, with the Fifth and Eighth Doctors going to great lengths to avoid dying in space. (PROSE: , ) Malika believed that her regenerative processes would simply not activate in the vacuum of space, as her new incarnation would simply die all over again, rendering the process futile. (COMIC: ) The Eighth Doctor instead recalled horror stories of Time Lords regenerating in such an environment, burning themselves out as their new bodies became increasingly twisted trying to "evolve" into something that could cope in a vacuum. (PROSE: ) However, safe regeneration from exposure to a vacuum was possible if the subject was returned to an oxygenated environment before the process initiated, with one Time Lord regenerating normally after being cast adrift in space before the War Doctor materialised his TARDIS around him and left him to regenerate in the ship's Zero Room. (PROSE: ) The Fifth Doctor once noted that the important thing in regeneration was that the brain remained intact, with an early Gallifreyan being killed for good when she was shot in the brain at close range with a 26th century weapon. (PROSE: )
Retro-genitor radiation was specifically created by the Daleks to inhibit regeneration. (AUDIO: ) The Daleks also used regeneration inhibitors within their gunsticks during the Last Great Time War (AUDIO: ) and equipped with Varga plants with similar inhibitors. (AUDIO: )
Certain types of radiation could be more dangerous to Time Lords than others. Roentgen radiation was relatively harmless so long as it was expelled quickly enough, (TV: ) and the Doctor was able to hold back his regeneration for several hours after being exposed to the radiation from the Immortality Gate. (TV: ) However, the radiation belt around Lakertya was uniquely deadly to Time Lords while safe for human exposure, (AUDIO: ) and the radiation around the blue crystals of Metebelis III caused so much damage to the Third Doctor that he required external aid to trigger his regeneration after spending ten years drifting in the TARDIS dying of exposure. (TV: , )
When the Sixth Doctor was exposed to radiation on a Cyberman ship, he ran the risk of triggering a tortured sequence of regenerations where he would rapidly exhaust his remaining lives as the radiation damaged his cellular structure so that his subsequent incarnations would still suffer damage even after regeneration; as with his third incarnation's death from the Metebelis radiation, he only survived because he returned to the timeless stability of the TARDIS and was kept in a form of temporal stasis until his body had recovered. (PROSE: )
The Fifth Doctor was not sure if he would be able to regenerate after contracting Spectrox toxaemia, and indeed the transition into his next incarnation occurred "not a moment too soon". (TV: ) It was implied that particularly serious blood loss could prevent regeneration altogether; Ruath was able to regenerate after draining her blood and sending it to Yarven via her TARDIS, (PROSE: ) but the Eighth Doctor and Romana II were both concerned that the Fourth Doctor would die for good after several vampires fed on him at once before the Eighth Doctor was able to give his past self a transfusion. (PROSE: ) Particularly traumatic damage could cause a Time Lord to suffer regenerative collapse, which would kill them immediately regardless of how many lives they had remaining; the Sixth Doctor almost suffered this fate after a confrontation with Zor, requiring Captain Jack Harkness to give him medical attention and take his place for a time until the Doctor had recovered. (AUDIO: )
Due to the Time Lords' reliance on artron energy to power the regenerative process, an artron inhibitor could prevent Time Lords from regenerating, as well as limit their ability to heal from damage; when Time Lord agent Cuthbert Simpson attempted to track and trap Compassion with an inhibitor, his injuries were so serious that it took him decades to recover even after the field preventing him from regenerating was deactivated. (PROSE: ) Some Time Lords, such as Yayani, had Abridgement Syndrome, which made them unable to regenerate. (PROSE: ) When the Doctor's TARDIS was damaged by a vitreous time storm, the subsequent effects on the Doctor due to his link to the ship nearly killed both of them until a past Doctor was able to donate the energy needed for the ship to heal itself. (AUDIO: ) By the Last Great Time War, the Varga plants evolved so that they possessed regeneration inhibitors which could kill a Time Lord instantly. (AUDIO: ) Dalek weapons also incorporated regeneration inhibitors, with the result that Daleks could kill Time Lords instantly, even if the High Council maintained the propaganda that regeneration would still be an option if Time Lords fell in battle. (AUDIO: )
In the early days of regeneration, the process was so disruptive to a Time Lord's DNA that regenerations were known to incorporate aspects of what the Time Lords had recently eaten before regenerating. While this defect had been corrected by the Doctor's era, the old Gallifreyan priest I.M. Foreman still had this defect in his system, resulting in his thirteen incarnations representing a wide range of genetic anomalies as he pushed his biodata envelope as far as it could go, culminating in his final incarnation "evolving" to become the vibrant new biosphere for an entire planet. (PROSE: )
Ideally, regeneration would be undergone within a low-grade telepathic field. The presence of another Time Lord was recommended to assist with any difficulties, and the newly regenerated Time Lord best remained in a state of total tranquillity for a time afterwards to allow the mind and body to properly readjust. (PROSE: )
=== Regenerative cycle ===
==== Number of regenerations ====
Time Lords usually had a limited cycle: twelve regenerations, consisting of thirteen incarnations, after which they would suffer permanent death, (TV: , , ) except insofar as their minds, uploaded to the Matrix, lived on as Matrix Lords. (PROSE: ) On occasions, the Doctor gave other numbers as the length of the basic Time Lord regeneration cycle. The Fourth Doctor told Romana that Time Lords had ninety lives, and that he had already gone through "about 130" of them; (TV: ) the Fifth Doctor, while in a state of confusion, later claimed the same thing. (AUDIO: ) The Eleventh Doctor told Clyde Langer that he could regenerate 507 times. (TV: )
As with most such "rules", there were occasional exceptions to the twelve regeneration limit: although Rassilon had originally found the twelve-regeneration cap to be absolute, forcing him to retreat into the Matrix as a disembodied mind to survive his final death, (PROSE: ) the High Council, at later points in history, was capable of offering Time Lords a new lease of life in the form of a new regeneration cycle. The Council offered a new regeneration cycle if he rescued the various incarnations of the Doctor from the Death Zone. (TV: ) Although he did not receive this award on that occasion, later in his life, he was resurrected by the Time Lords (AUDIO: , TV: ) as part of a deal they made with a future version of himself, (AUDIO: ) and was able to regenerate on at least three more occasions. (COMIC: , TV: , ) It was indicated that the Master possessed at least one more regeneration after this as he told his future self "don't bother trying to regenerate" after mortally wounding her with his laser screwdriver. (TV: ) Missy went on to cheat death by using an Elysian Field to reconstruct her body at an atomic level, granting her a new regeneration cycle. (AUDIO: )
The Time Lords also granted the Eleventh Doctor a new cycle of regenerations before he could die for the final time, having used up all twelve of his regenerations in his first cycle; (TV: ) the Twelfth Doctor, (TV: ) the Master (TV: ) and even Rassilon himself were uncertain as to how many regenerations the Doctor now possessed. (TV: )
Aside from being granted a new cycle, there were other ways to gain regenerations. Having used up all of his natural regenerations, the Master was able to gain an extra one by using the Source to merge with Tremas, (TV: ) undergoing a regeneration into a new body, (AUDIO: ) then later gaining another regeneration after being cured by Tzun nanites. (PROSE: ) However, these artificial means of adding regenerations was not permanent and eventually the Master reverted back to his decayed self. (AUDIO: )
's discoveries about the Timeless Child in the Matrix suggested that the Child had originally possessed more regenerations than the typical twelve, and that it had been the Second Tecteun's decision, when the Founder had shared the genetic gift of regeneration with his people, to limit the common folk's regenerations to a maximum of twelve times. The Master believed that the Child had later become the Doctor, who had gone through a number of lives which even he couldn't even guess at. (TV: )
==== End of a regeneration cycle ====
Despite not being able to regenerate any further, a Time Lord in their final incarnation retained a small amount of regeneration energy; just enough to mend broken bones once. (TV: ) Time Lords could will themselves to die by attempting to regenerate when they had no more regenerations left to use, as Azmael who was hosting the evil consciousness of Mestor, chose to do so to prevent it from escaping. (TV: ) The Eleventh Doctor likewise threatened to use regeneration to hold off Mr Clever from taking over his mind, fully aware that he had expended his first regeneration cycle's allotted lives. (TV: ) A Time Lord on their last regeneration could will themselves to effect a pseudo-regeneration which would cause their body to vanish into thin air. (TV: )
If they attempted to regenerate in earnest beyond their thirteenth and final body, a Time Lord's flesh could break down into degenerate matter and then into random molecules, as was the case for one particular Time Lord. (COMIC: ) The Thirteenth Doctor believed that attempting to regenerate "one time too many" was what had once caused the Master to degenerate into (PROSE: ) a barely-alive, emaciated, ambulatory cadaver, (TV: , ) although other accounts suggested that this skeletal form was instead simply the Master's thirteenth incarnation after sustaining debilitating injury, (AUDIO: ) or indeed an incarnation of the Master who had simply been injured in a fashion that took away his ability to regenerate. (PROSE: )
=== Transference of regenerative energy ===
When the Third Doctor was too weak to regenerate, Cho-Je gave him a "little push" to jump-start the process. However, doing so scrambled the Doctor's brain a bit. (TV: )
In an attempt to end their perpetual cycle of rebirth, Mawdryn and his crew attempted to force the Fifth Doctor to sacrifice all eight of his remaining regenerations so that they could take his 'deaths' for themselves. Although the Doctor rejected that request because he was unwilling to essentially kill himself eight times over in order to save this crew from their own mistake, he was willing to do so in order to cure his companions of an infection they had contracted from exposure to Mawdryn's crew. However, the same necessary energy was released when the Brigadiers of 1977 and 1983 made contact with each other, the temporal energies released in the subsequent paradox serving the same purpose as the Doctor's eight regenerations. (TV: )
While regeneration was a natural Time Lord function, it was not an intrinsic part of their genetic makeup that could be acquired through simple DNA samples. When the Forge created a clone of the Sixth Doctor, the most successful clone retained the Doctor's knowledge but was incapable of regenerating, although this may have been due to flaws in the Forge's cloning technology. (AUDIO: ) The Doctor was initially uncertain whether his "daughter" Jenny (grown from harvested genetic material of his tenth incarnation) could regenerate, and when he witnessed her dying of a gunshot wound, commented she wasn't "enough" like him with a fatalistic tone. Jenny later returned to life (unbeknownst to the Doctor) in a burst of golden shimmering energy, but without changing her face; the energy resembled regeneration energy, but also the life-giving gasses of the Source. (TV: ) According to one account, the Doctor's new golden appearance was due to the Restoration from his saviour. (PROSE: )
After was executed by the Daleks and transferred his essence into a human body, he attempted to use the Eye of Harmony in the Doctor's TARDIS to transfer the Eighth Doctor's five remaining regenerations to him to restore himself to full life. This plan failed when the Doctor's ally Grace Holloway set the TARDIS into temporal orbit, severing the link between the Eye and the Master, returning the Doctor's regenerations to him and leaving the Master once again trapped in a dying body, which was subsequently lost when he fell into the Eye. (TV: )
During the War in Heaven, the Time Lords granted many of the lesser species the ability to regenerate, creating the regen-inf. (PROSE: , )
When the Eleven discovered the Matrix print of the Time Lord scientist Artron, he was able to use the knowledge on the Matrix print and the Crucible of Souls - a space station previously designed to absorb life energy from the dying universe - to grant the entire universe of the present the ability to regenerate to become a new food source for the Ravenous. The Doctor and three different incarnations of the Master were able to undo the Eleven's actions and restore mortality to the universe. (AUDIO: )
During the Last Great Time War, the Time Lord Vassarian was captured by the Sontarans after he entered the Eternity Cage of his damaged Battle TARDIS as he started to regenerate, leaving him trapped in the moment of his own regeneration. The Sontarans were able to use the resulting artron energy released to power various temporal weapons, with the goal of opening a third front in the Time War, but the War Doctor was able to make telepathic contact with Vassarian as his mind was still active on some level. While technically frozen in time, Vassarian revealed that he had lost so much energy through the Sontarans' actions that he would be unable to regenerate. The War Doctor helped him end his life so that the Sontarans would be destroyed by the Daleks. (AUDIO: )
When the Third Doctor was drawn to a time period shortly after the Tenth Doctor had regenerated, the Tenth Doctor unknowingly drew on the energy of his past self to stabilise his own regeneration simply because the two Doctors were in close proximity to each other without either Doctor coming face-to-face. The Third Doctor described the experience as energy osmosis as the weaker incarnation took energy from the stronger. The process caused the Third Doctor to feel a brief fatigue before returning to normal, whereas the Tenth Doctor was restored to full health. (PROSE: )
In one instance, the Tenth Doctor used up his first cycle's eleventh regeneration while still keeping the same face by channelling it into a hand (TV: , ) which had been sliced off by the leader of the Sycorax, (TV: ) allowing himself to heal his body, yet avoid physical changes. This energy remained active and was accidentally interacted with by a human, Donna Noble, triggering a two-way human-Time Lord meta-crisis which caused the hand to regenerate the missing body of its owner, creating a human-Time Lord copy of the Doctor and causing Donna to gain the mind of a Time Lord. However, the presence of two minds inhabiting Donna at once nearly destroyed her and the Doctor was forced to block all memories of him from her consciousness to stop her Time Lord half from remaining active. (TV: ) Donna would later go on to have a child, Rose Noble, who inherited part of the Metacrisis from her mother. When the Fourteenth Doctor was forced to reactivate Donna's memories to stop Beep the Meep from killing millions, Donna did not dies because the Metacrisis was now split in Rose, delaying her death from it. Rose, her Time Lord half likewise activated, then chose alongside Donna to simply let go of the regeneration energy, reverting them both to fully human. (TV: )
Dead Time Lords could be revived with regenerative energy, though the amount of energy required to do this was very large and took a physical toll on the donor. Doing this, Melody Pond, in her third incarnation, sacrificed her ten remaining regenerations to save the Doctor's life after he was dying from a poison that would normally immobilise his ability to regenerate, and was hospitalised as a result. (TV: )
Despite using up all twelve of his regenerations, the Eleventh Doctor possessed enough regenerative energy to heal River Song's broken wrist, although she was angered at what she considered a waste of the energy. (TV: )
The Twelfth Doctor attempted to donate a small portion of regenerative energy to the dying Davros to give him the strength to see a final sunrise, speculating that this would cost him an arm or a leg at some future date (or make him diminutive in stature), but Davros used this opportunity to siphon regeneration energy from the Doctor, and transmit it to all the Daleks across Skaro. While the Daleks grew stronger, Davros gained several more years of life. (TV: ) It is unknown if the Doctor suffered any long-term consequences from this, as he was subsequently able to regenerate without complication, (TV: ) although the Thirteenth Doctor noted that "[her] legs definitely used to be longer" after attempting to jump between two cranes. (TV: )
An illusionary version of the Twelfth Doctor attempted to temporarily cure his current blindness by transferring energy from his own future, noting that it may cost him the ability to regenerate in a worst-case scenario. The long-term consequences of this were not important as this Doctor was only a digital recreation. (TV: )
The Twelfth Doctor also demonstrated the ability to release regenerative energy at will without transferring it to anyone else, instead simply allowing it to dissipate. This allowed him to essentially fake a regeneration without changing. It is unclear how much energy this used, or how it may have affected his ability to regenerate in the future. (TV: )
In order to trigger a retro-regeneration in the Thirteenth Doctor's body, Yasmin Khan and Inston-Vee Vinder, guided by an AI hologram of the Fugitive Doctor, triggered the CyberMasters to regenerate and then drained all of their regeneration energy into the 's machine. Along with successfully triggering the retro-regeneration, this also appeared to drain the CyberMasters of their regeneration energy entirely, leaving them truly dead. (TV: )
=== Control over regeneration ===
Generally, the regenerative process triggered itself when a Time Lord was too badly injured to survive; however, in some cases, Time Lords exercised control over the process. Romana I seemed to regenerate on a whim, (TV: ) while Azmael deliberately attempted a thirteenth regeneration to end his life. (TV: ) When badly injured without actually sustaining regeneration-inducing injuries, the regenerative platelets in a Time Lord's blood could activate to accelerate their ability to heal, allowing them to recover from serious injuries more quickly than a human would, (AUDIO: ) although particularly serious yet non-fatal damage would require the Time Lord to enter a healing coma to recuperate. (TV: , PROSE: )
When Rallon was taken as a host by the Toymaker, he began to die after centuries bonded to the powerful entity, but was eventually able to die as himself by triggering all twelve of his regenerations at once after receiving a boost of telepathic energy, expelling the Toymaker from his body even if the strain of it killed him. After this mass regeneration, Rallon's Watcher - which had previously manifested as part of Rallon's plan against the Toymaker - merged with the Toymaker in Rallon's place, with the Watcher essentially acting as a new incarnation of Rallon, thus causing a similar change to the Toymaker's personality as though he had regenerated himself. (PROSE: )
The degree of control that Time Lords had over their end appearance was unclear. stated, "Most Time Lords are at the mercy of fate after death." She desired the ability to definitively control the outcome of her appearance upon regeneration and attempted to learn how to do this by studying Koturian Phasing. Her attempt failed, however, because she was not in love with the man she was engaged to, which was the catalyst for Phasing. (PROSE: ) The Master had the ability to control the appearance of each of their regenerations. (PROSE: ) Indeed, the mortally wounded War Master decided that would be "young and strong" to match the Tenth Doctor. (TV: ) In contrast, Missy claimed to have had no influence over her then present form. (AUDIO: )
Melody Pond announced she was "focusing on a dress size" moments before her final regeneration. She also commented that she might "take down the age a bit, just to freak people out," although she did not elaborate whether this was a joke or a literal intention. (TV: ) Romana I seemed adept enough at the process to custom design her new form during what seemed to be a voluntary regeneration. The Doctor criticised Romana II for taking on the form of another person, suggesting such things were not unheard of. (TV: ) On an earlier occasion, Lord Roche was able to influence his next incarnation to be a double of the Third Doctor's appearance when he regenerated after being hit by a bus despite having only briefly seen the Doctor. (PROSE: ) When Glospin attempted to frame the First Doctor for the murder of Quences, he was able to deliberately regenerate into a duplicate of the Doctor after taking a genetic sample during a fight. (PROSE: ) Lake observed his fellow clones sometimes exhibited control over aspects of their next bodies and realised he could influence his own regeneration by focusing on a specific appearance he desired as he was regenerating. He used this knowledge to influence one of his incarnations into the identical form of a man he murdered in order to steal his identity. (AUDIO: )
When it came to changing sexes during regeneration, however, a Time Lord had no say in the matter, unless the regeneration was triggered willingly. (COMIC: )
In contrast to Romana, the Doctor did not seem to have much control over their post-regeneration appearance; after their fourth regeneration, the Fifth Doctor commented, "That's the trouble with regeneration, you never quite know what you're going to get." (TV: ) The Ninth Doctor restated this sentiment immediately prior to their tenth regeneration, referring to the process as "a bit dodgy". (TV: ) They also nearly always examined themselves or asked about their appearance. (TV: , , , , , , ) Both the Seventh (TV: ) and Tenth Doctors (TV: ) referred to regeneration as "a lottery".
While skilled Time Lords could choose their new form with a voluntarily induced regeneration, the process could go horribly wrong and leave the Time Lord in a severely misshapen body. This problem could be exacerbated by the Time Lord immediately starting another regeneration instead of obtaining medical assistance, amplifying the defects in the regeneration. The end result of these abortive regenerations was inevitably a mutated monstrosity that could only be put out of its misery by complete disintegration. (PROSE: )
In cases where Time Lords could not choose their new appearance, it appeared that their bodies still had some degree of natural "control" over the forms they would take upon regenerating. The Third and Seventh Doctors were once given glimpses of what their next incarnations would look like without actually meeting their future selves, when the Third was briefly possessed by the Nurazh and nearly regenerated before his injuries were healed (PROSE: ) and when the Seventh encountered Elizabeth Klein and learned about her relationship with the version of him that existed in the timeline where Ace died at Colditz. (AUDIO: )
At least one of the infinite parallel universes of "possible space", (COMIC: ) it was said that a Time Lord's new form was chosen by their "unconscious". (PROSE: ) Indeed, after the Twelfth Doctor's regeneration, he believed that he recognised his new face from somewhere, (TV: ) but it took some time until he recognised it (TV: ) as the face of Caecilius, (TV: ) speculating that he "chose" the face to remind himself that his purpose as the Doctor was to save people, irrespective of other forces (such as those watching over history) "having a problem with that". (TV: ) 
Some Time Lords were capable of momentarily regenerating, or partially regenerating. Though this could use up a lot of regenerative energy, it would give the Time Lord a new set of genes, allowing them to fool genetic sensors. The Seventh Doctor used this method on the planet Purgatory to fool the genetic scanner used by the Imperial Landsknechte. (PROSE: )
Forcing an individual to regenerate could be used as a form of punishment and in these cases, the new appearance could be chosen or influenced by the condemned. (TV: ) Granting additional regeneration cycles (TV: , , ) or removing any remaining regenerations (TV: ) was also possible. Rassilon's gauntlet could be used to remove regenerations, or at least force a Time Lord to repeatedly regenerate until their remaining lives were exhausted. (TV: )
The Sisterhood of Karn had elixirs that could trigger and control regeneration in a Time Lord who was dying and unable to regenerate normally or, in extreme cases, already dead. These elixirs could determine traits to be held by the new incarnation such as appearance, sex, apparent age, and personality. (TV: ) Though some "elixirs" were fake; a Time Lord could be tricked into willingly regenerating into the person they wished to become. (PROSE: )
With effort, Time Lords could resist regeneration, effectively committing suicide. (PROSE: ) refused to regenerate after being shot, ostensibly to avoid becoming the Tenth Doctor's eternal prisoner. (TV: ) Similarly, the Fifth Doctor once threatened System with resisting regeneration to stop the device from learning the biological details of the act. (AUDIO: ) This was not always an option, however, as the Sixth Doctor noted fearfully that while his companion could die only once, he might repeatedly regenerate and live out all of his lives when the TARDIS stalled in space. (TV: ) Both the First and Twelfth Doctors at first refused to regenerate, with the First Doctor's appearance being slightly changed as a result, but eventually relented and went on to become their successive selves. (TV: )
Rassilon had discovered a form of true immortality beyond the regenerations known to the Time Lords, but kept this a secret, believing it would be too dangerous to share. He went to the extreme of entombing the secret with himself in the Death Zone of Gallifrey and petrifying all those who came to inquire of the method. Borusa described Rassilon's immortality as a "timeless, perpetual, bodily regeneration". (TV: )
The ancient Gallifreyan scientist Artron found means of perfecting his own version of the regenerative process, which allowed the subject to regenerate swiftly but retain their original appearance and personality, with no limits on the number of times they could regenerate. The Time Lords sent the War Master to retrieve the Matrix print from the Eleven so that they could use this knowledge in the Time War. The Master agreed to this deal in return for them restoring his past self's ability to regenerate, although the Time Lords insisted that he only give himself a new regeneration cycle under the standard rules. (AUDIO: )
After deciding to help the Doctor, Missy stabbed in such a way that the wound was "precise", forcing him to regenerate but giving him a period of time before the process was triggered. (TV: )
Donna Noble suggested that the Thirteenth Doctor's regeneration into the Fourteenth Doctor was because of how emotionally exhausted the Doctor was after everything that they had been through over their lives. The Doctor subconsciously wanted to return to the face of their tenth incarnation and find Donna to come home. (TV: )
=== Forced regeneration ===
It was possible for Time Lords to inflict a forced regeneration on others, triggering a regeneration as a punishment and even deliberately influencing the form of the next incarnation. When the Time Lords sentenced the Second Doctor to exile on Earth, they initially attempted to give him a choice about his next appearance as part of the accompanying sentence of regeneration, but the Doctor tried to escape this choice by rejecting the offered faces and his subsequent regeneration was seemingly random. (TV: ) 
Using technology he had stolen from the now-destroyed Gallifrey, the Master used an artificial planetoid to gather enough energy to allow him to force a regeneration on the Thirteenth Doctor, causing her to regenerate into a form that was a near-exact copy of the Master himself. However, this regeneration was soon established as being particularly unstable, allowing the Doctor's allies to capture the Master/Doctor and use that same equipment to undo the forced regeneration so that the Doctor was restored to her previous incarnation. It is unclear if this transition to and from her temporary state as the duplicate Master would count as the Doctor using a regeneration or two, as the process was explicitly described as being unstable to the extent that the Thirteenth Doctor spoke with manifestations of her past selves in her mind who suggested that she was resisting the "need" to complete the change in hopes of stopping the Master's plan. (TV: )
=== Bi-generation ===
Bi-generation was a rare mutation of regeneration that was believed by the Doctor to be merely a myth. After being mortally wounded, instead of changing directly into the new incarnation, the new incarnation would instead split from their previous self, existing as a separate entity while the original incarnation involved would be healed of their fatal injuries. (TV: )
After being mortally wounded by the Toymaker, the Fourteenth Doctor underwent a bi-generation instead of a regular regeneration. The regeneration at first appeared to be normal, but when the regeneration energy disappeared, the Fourteenth Doctor remained himself, although he felt something different. At his request, Donna Noble and Melanie Bush each pulled on one of the Fourteenth Doctor's arms, causing the Fifteenth Doctor to begin emerging from his body. The two Doctors then finished the bi-generation by shoving each other away from themselves. The exact nature of the process was unclear, though the Fifteenth Doctor later claimed that he was now at peace due to the Fourteenth having "fixed himself" by settling down, likening it to "therapy in reverse". (TV: ) 
=== State of grace ===
According to the Twelfth Doctor, there was a period of time that he called "a state of grace" when a dying Time Lord could resist regeneration for a period of time without consequence and were restored to full strength. During this period of time, the Time Lord had to choose whether or not they would ultimately regenerate or else they would grow weaker as time passed by. At this period's end, the Time Lord would either regenerate or die permanently. (TV: ) While a state of grace could be voluntary, some forms of death could induce a similar state unless they received aid. When the Third Doctor contracted radiation poisoning on Metebelis III, (TV: ) he spent ten years drifting in his current form in the TARDIS before he finally died upon returning to UNIT, (PROSE: ) only regenerating with the aid of K'anpo Rimpoche. (TV: )
The First Doctor, fearing the change, held off his own regeneration for several hours. However, unlike his future incarnations, the Doctor's face did not stay the same, becoming "mixed up" while in the state of grace. When the Doctor regenerated, he passed out as his state of grace ceased. (TV: ) However, his regeneration was comparatively peaceful compared to when his future selves regenerated after halting the process. (TV: ) The Thirteenth Doctor also underwent a similarly peaceful regeneration after only using the state of grace for a short period of time to say goodbye to Yasmin Khan. (TV: )
The Fifth Doctor was able to hold off his regeneration from Spectrox toxaemia for several hours (AUDIO: ) while trying to retrieve the bats' milk needed for the antidote, but finally accepted the need to regenerate when he was only able to acquire enough for his companion, Peri. (TV: )
The Ninth Doctor momentarily delayed his impending regeneration to explain what was happening to Rose Tyler. (TV: )
After subjecting his body to a lethal amount of radiation, the Tenth Doctor delayed the regenerative process long enough to revisit each of his former companions, (TV: ) including those of his past selves, (TV: ) before he finally regenerated, which severely damaged the TARDIS. A few minutes before the regeneration began, his "state of grace" ended causing the Doctor to experience excruciating pain, resulting in him collapsing to the ground, barely possessing the strength to reach his TARDIS. (TV: )
When the Eleventh Doctor was granted a new regeneration cycle on Trenzalore, he was able to use the energy from the resulting "reset" to regress his body to a younger state and hold back the regenerative process for a time. (TV: ) During such, he phoned his personal future to ensure Clara Oswald stayed with his future self, (TV: ) and later said goodbye to his companion before finally undergoing a full regeneration. (TV: )
When severely injured by a Cyberman, the Twelfth Doctor was able to resist regeneration for several weeks despite struggling to walk. He further resisted it despite numerous Cybermen mortally wounding him, buying himself time to ignite Floor 0507. However, he struggled to hold it off when revived in the TARDIS, nearly regenerating completely. (TV: ) He then encountered the First Doctor, who was also in a state of grace, holding back his regeneration as he feared regenerating. Throughout this time, the Twelfth Doctor steadily grew weaker, nearly collapsing at one point while at Villengard and having to sit down for a few minutes to recover. After the adventure, both Doctors chose to regenerate. While holding his regeneration back a little longer to make an advisory speech to his future incarnation, the Twelfth Doctor continued to grow weaker and collapsed to the floor just before his regeneration occurred, though he managed to stand up once more by leaning on the TARDIS console to help him to his feet. Similar to the Tenth Doctor's regeneration, the Twelfth Doctor regenerated explosively, causing the control room in the TARDIS to explode. (TV: )
=== Difficult or unusual regenerations ===
==== Regenerative difficulty ====
While most regenerations seemed to cause moments of mental instability, with temporary amnesia often noted, some offered particularly profound instances of physical peril. The Fifth Doctor feared that his regeneration was "failing" when he found himself reverting to previous personas, and could only be righted with the use of the TARDIS Zero Room. Ambient complexity could also contribute to the failure of a regeneration. (TV: ) The Eighth Doctor claimed that anaesthesia had "nearly destroyed the regenerative process" during his seventh regeneration as an explanation for the particularly severe amnesia he suffered afterwards. (TV: ) During the Tenth Doctor's post-regenerative state, he suffered an arrest in one of his hearts and began to exhale regenerative energy when Rose Tyler revived him too early. After this, he said that he was having a neural implosion, and slipped into a coma-like state for most of the day. (TV: ) Upon hearing of this, the Third Doctor suggested that his future self was suffering from a regeneration crisis. (PROSE: )
Regeneration, especially later ones, could be painful. Melody Pond screamed during one regeneration, (TV: ) as did the Master during his transition into . (TV: ) The Ninth Doctor winced in pain as his regenerative energy spiked, (TV: ) the Tenth Doctor also appeared to grimace in pain during the process, and the Eleventh Doctor screamed as he emerged from the regeneration. (TV: ) Once, Sarah Jane Smith asked the Eleventh Doctor if his last regeneration had hurt. After trying to deflect the question, he quickly said, "It always hurts," before, in the same breath, continuing with the task at hand. (TV: ) The Eighth Doctor's regeneration was painful due to the circumstances, but he wanted it so. (TV: ) After being asked if regeneration was painful when she described the process, the Thirteenth Doctor replied that "you have no idea." (TV: )
In some cases, it was possible for the regenerative process to be restarted by another Time Lord if it failed, such as when Cho-Je gave the Third Doctor's body "a little push" to initiate the regeneration process after he was exposed to the radiation of the Metebelis crystals, although he warned that the new Doctor would be somewhat shaken up as a result of this method. (TV: )
After suffering damage to his body during his plan to take over the Doctor's body with regeneration, 's own body began to fail and was later crushed by a boulder. (TV: ) The Toymaker revealed to the Fourteenth Doctor that the Master was dying and had to play a game against the Toymaker to survive, but lost and was trapped in his gold tooth. (TV: )
==== Reversal ====
There were many ways to reverse a regeneration. One way involved the sacrifice of another, causing the regeneration to reverse. One example of this was when the Third Doctor had an encounter with the Nurazh. As the Doctor battled the Nurazh's main host, the two fell off a building, killing the Doctor. As the Third Doctor (nearly) regenerated into the Fourth, the Nurazh possessed the Time Lord's body; however, it found itself unable to cope with the two Time Lord minds within the body and it soon perished, restoring the Doctor to his previous incarnation in the process. (PROSE: )
When trapped in a dimensionally-unstable pocket universe created and controlled by Iam and , the Sixth Doctor's morphic print was destabilised, causing him to unwillingly and painfully regress back through his previous selves as his body sought a stable morphic print. He was forced to rely on the stabilising atmosphere of the TARDIS and a personal morphic stabiliser he designed to operate in this realm until it was returned to the real universe. (PROSE: )
Some Time Lords of the first rank attempted retro-regeneration, reverting from their current incarnation back into a prior body, but this procedure was relatively rare, to the extent that the Sixth Doctor was unable to recall any examples of it. (PROSE: ) The Tenth Doctor once reverted into the Ninth Doctor when an artefact reversed his local time field. Moments later, he changed back, but wondered if he got back the regeneration he wasted. (COMIC: )
On rare occasions, it was possible for Time Lords to deliberately allow themselves to mentally regress back to the personas of previous selves while remaining the same incarnation physically. When he was trapped in Iam's unstable realm, the Sixth Doctor was able to use his current morphic instability to allow the Third Doctor's persona to take control, allowing him to draw on his past self's skill for hand-to-hand combat. (PROSE: ) On another occasion, the Seventh Doctor used the TARDIS telepathic circuits to bring the Third Doctor to the fore so that he could use his past self's skill with technology to disarm a dangerous bomb, although his control sometimes slipped as his current self tried to assert itself, resulting in the Third Doctor referring to his current associates by the names of his own companions. (PROSE: )
When the Master inflicted a forced regeneration on the Thirteenth Doctor that transformed her into another version of himself, the Doctor was able to mentally resist this transition. Manifestations of her past selves observed the strength required for her to resist crossing over completely, and the Doctor also noted that forced regenerations would be even more unstable than usual. Her companions were subsequently able to capture the Master and use the Master's equipment and the regenerative energy of the Cyber-Masters to restore the Doctor to her previous incarnation. (TV: )
==== Regenerative dissonance ====
Considered as a rare mental illness, Time Lords might not lose their past personas when they regenerate. As a result, these Time Lords acquired new physical bodies, but the past personas remained conscious and active in their minds, rather than simply retreating into the Time Lord's subconscious. These past incarnations thrived and accumulated inside the current incarnation's head, fighting over control of the physical body. One known Time Lord who had this illness was the Eleven. (AUDIO: ) Immediately after regeneration, the previous incarnations would be mentally weaker and more disorientated, but they would eventually assert themselves and resume the Eleven's warped sense of mental balance. (AUDIO: ) Other Time Lords were known to suffer from this illness, but they often committed suicide as they couldn't cope with the voices. The Time Lord who lasted the longest with this condition (other than the Eleven) died after shooting out both his hearts with a staser in his eighth body. (AUDIO: ) The very nature of this illness also had an unusual side-effect of somehow affecting the regeneration energy produced by the Eleven, with the result that he was the only known Time Lord the Ravenous could not feed off. (AUDIO: )
==== Avoiding change ====
A Time Lord could avoid the change of appearance and personality caused by regeneration by focusing the regenerative energies into a "bio-matching receptacle", as the Tenth Doctor did with his own severed hand. The hand siphoned off the excess energy that would have changed his appearance while the Doctor used just enough to heal himself (TV: ) from the injury sustained from a Dalek gunstick. (TV: ) This resulted in the appendage storing enough residual energy to grow an identical Time Lord when it came in contact with Donna Noble soon after. (TV: ) As a result, the Doctor used up a full regeneration (his eleventh of twelve overall), (TV: ) but kept his appearance, allowing him to avoid the usual post-regenerative confusion and disorientation experienced in the past. (TV: )
During the time when he controlled the Source of Traken, (TV: ) the Master was able to use the Source to heal his injuries in place of regenerating, noting that this process was far smoother than regeneration as it avoided sacrificing the healthy tissue in the process, although this method eventually proved short-term when he expended the last of the Source. (PROSE: )
The regeneration process could also be delayed to allow healing. The Second Doctor was shot in the head when confronted by guards on Skybase, causing damage to his skull and frontal lobe; and the subsequent fall broke his nose, jaw, right femur, and collarbone, along with causing some spine damage. He began to regenerate, but an injection of Shiner DNA delayed the regeneration and kept him alive long enough for his body to go into a six-month healing coma to recover on its own, although he was briefly certain that he had regenerated when he woke up. (PROSE: ) When the Seventh Doctor deliberately affected himself with light wave sickness to save the Spiridons from the Daleks, he briefly believed that he was going to regenerate until he retreated to the TARDIS, his body spending some time fighting between its cellular paralysis and natural desire to regenerate until it stabilised in his current self. (AUDIO: )
When his second heart was extracted by Sabbath and placed in Sabbath himself, the stolen heart created a link between the Eighth Doctor and Sabbath that rendered the Doctor essentially immortal; as his second heart was still beating in Sabbath's chest, the Doctor could survive normally fatal injuries, such as having his chest crushed by sandbags or being stabbed in his remaining heart, without changing, although he would go into a near-death state until his body could heal. However, it was unspecified if there were any limits to this connection - the Doctor only needed to use it when he and Sabbath were on the same planet at the same time in the same city - and the connection was lost when Sabbath tore the Doctor's heart out of himself. (PROSE: , )
The ancient Gallifreyan scientist Artron was able to devise a system of perpetual regeneration where the subject would not need to change their appearance during the process, but even after this knowledge was regained during the Time War with the recovery of Artron's Matrix print, the Time Lords were never shown putting it into full practise, save for granting the Master a new set of regenerations in return for his assistance while insisting that he limit himself to the standard thirteen lives under the usual rules. (AUDIO: )
==== Cross-species transformations ====
I.M. Foreman, an early Gallifreyan (but not a Time Lord), absorbed the DNA around him and underwent indescribable changes as a result of mutations, transcending sex, species and even physical existence itself. (PROSE: , ) Romana, prior to her regeneration into her second incarnation, appeared to take on a humanoid blue-skinned form, (TV: ) although one account held that the TARDIS itself, rather than Romana, had adopted this shape. (PROSE: ) Former Cardinal Zero regenerated into the form of the avian species whose planet he had taken residence on. (AUDIO: ) Although the Doctor's actual tenth self was, like the Time Lord's previous and later bodies, indistinguishable from a human, the previous incarnation of the Doctor had mused that his next body "might have two heads… or no head" before regenerating. (TV: ) Novice Hame heard stories about animal incarnations of the Doctor. (WC: ) There was a cat incarnation of the Doctor in an alternate universe. (COMIC: )
==== Aborted regeneration ====
Occasionally, a regeneration would fail and the process would abort. Though the Time Lord would have regenerated, they would be severely deformed. Though Time Lord technology could treat this, on some occasions the damage would be too severe to fix.
Regenerative collapse was a potentially fatal complication of regeneration. Mortally wounded by Zor, the Sixth Doctor's body attempted to regenerate when he found himself on the brink of a regenerative collapse. Fortunately, he was found and healed by Captain Jack Harkness, saving his life as well as stopping him from regenerating. (AUDIO: )
After being shot by the War Lords, the War Chief was barely able to survive. While being returned to the War Lords' planet, his body attempted to regenerate. Due to the massive injuries and the lack of medical care, this regeneration aborted. This resulted in two conjoined individual bodies, poorly fused together, and also apparently compromised his ability to regenerate ever again, preventing him from simply regenerating once more to solve the problem. (PROSE: )
==== Iterative regeneration ====
During the Last Great Time War, Rassilon experimented on other Time Lords, retro-evolving their timelines and connecting them to the time vortex, in order to build a possibility engine - a machine to question about decisions to make during the conflict. A side effect of the process on the so-called Interstitials was the trapping in a loop of an iterative regenerative cycle, which caused their appearance to enter a state of constant flux among their different incarnations. (PROSE: )
==== Blocked regeneration ====
Even if a Time Lord's body was damaged to the point that regeneration became impossible, their cells would continue attempting to do so, making the actual process of death very slow; it took each copy of the Twelfth Doctor imprisoned in his Confession Dial "about a day and a half" to die after being attacked by the Veil. (TV: ) There were, however, ways to circumvent this. A "full blast" of the Master's laser screwdriver killed Missy within a minute, with no visible wound and not even the beginnings of a regeneration. (TV: )
More simply, dealing a second killing blow to a Time Lord while they were already regenerating could prove fatal, as (after beginning to regenerate from a first shot) the Teselecta duplicate of the Eleventh Doctor at Lake Silencio appeared to die instantly when shot mid-regeneration. (TV: ) The Sword of Never could render all twelve of a Time Lord's regenerations useless. (PROSE: )
=== Attitude toward regeneration ===
As noted above, regeneration was not guaranteed. The Doctor on numerous occasions believed they were at risk of actually dying. Even with regeneration a possibility, the Doctor came to feel such a change as being a "death". In recollecting the events surrounding the Master's attempt to steal the Eye of Harmony, the Eighth Doctor referred to his incarnations as "lives". (TV: ) The Doctor's third, (TV: ) fourth, (TV: ) ninth, (TV: ) tenth, (TV: ) and twelfth (TV: ) incarnations referred to their regenerations as the end of their life. The Twelfth Doctor also referred to regeneration (though not his own) as the same as death, but also stated that to Time Lords, death was simply "man flu". (TV: ) When faced with regeneration himself, however, this Doctor truly valued his life, resisting the process as he didn't want to change. (TV: ) The First Doctor held similar reservations, disliking the change he would undergo. After seeing what his future would bring though, he felt more comfortable, embracing the change as he lost consciousness. (TV: ) By contrast, the Thirteenth Doctor ultimately accepted the change, wishing the next Doctor well after a significant victory over the Daleks, the Cybermen and the Master with the aid of various old friends. (TV: ) The Fourteenth Doctor likewise accepted the process, assuring Donna that he was not actually dying. (TV: )
In fact, the Doctor sometimes seemed to regard their previous incarnations as different individuals, capable of interacting and working with each other. (TV: , , , , , ) However, they still regarded their other selves as them, to the extent that their seventh incarnation became ashamed of the actions of his sixth self, going through a period of keeping his memory of his previous self locked up in his mind (PROSE: ) until he accepted that he was the Doctor in all of his incarnations, and forgave his past self's sins after he nearly died after being shot by an arrow. (PROSE: ) Younger or older Doctors could also disapprove of their other selves, such as the Fifth Doctor being horrified when he witnessed what the Seventh Doctor was capable of, (PROSE: ) the Eighth Doctor being ashamed at the manipulations of his past self, (AUDIO: ) the Third Doctor regarding his immediate predecessor as a distraction who would actually make him less effective, (TV: ) the Tenth Doctor expressing a rather low opinion of his previous self, considering him to be violent due to being "born in battle", (TV: ) and the Twelfth Doctor saying that his first incarnation was "rude to people" in his early days. (TV: ) The Missy and Harold Saxon incarnations of the Master grew to outright despise each other, despite having grown attracted to each other when working together, due to their juxtaposed view of the Doctor, to the point that they actually killed each other. (TV: )
At the same time, meeting other Doctors could allow other incarnations the chance to re-evaluate their opinion of themselves, such as the Eighth Doctor coming to admire the Sixth Doctor where his seventh had feared his predecessor's dark potential, (PROSE: ) and the Tenth and Eleventh Doctors recognising that the War Doctor was a true Doctor despite denying him for years. (TV: )
The Twelfth Doctor was also rather fond of the First Doctor, in a way very much tied to their shared identity; presented with this embodiment of his younger days, the Twelfth Doctor was amused at the First's old ways (such as how he still called the TARDIS "the Ship"), and how he looked wearing the sonic sunglasses. He was, nonetheless, incredibly embarrassed by his original incarnation's occasional sexist remarks. The First Doctor's reaction to his future was much less warm; he was dismayed at learning the Twelfth Doctor played the electric guitar, and disappointed in the Twelfth Doctor's lacklustre treatment of their TARDIS (deeming the new decoration "hideous" and expressing dismay at the dirtiness of the console room, which he attributed to the absence of Polly Wright, who, in his days, cleaned the TARDIS for him). He also criticised the Twelfth Doctor's over-reliance on technology over his own intellect, and his need to always boast about his plans. As a whole, the First Doctor was, at first, horrified to learn he would eventually become a "Doctor of War". However, he grew to admire his future self, believing their actions were for the greater good rather than malicious purposes as he initially believed. (TV: )
Most other Time Lords never expressed any strong opinions about their other incarnations as they had never met their other selves. However, the Twelfth General noted an immediate dissatisfaction with her predecessor shortly after her regeneration. (TV: ) More notably, when the Time Lord Straxus learned that he would become the insane Kotris in his next incarnation, he was horrified at his next self, proclaiming that Kotris was a psychopath, although Kotris claimed that his insanity was the result of Straxus' insanity and self-loathing. However, despite his disgust at Kotris's actions, Straxus only made a few half-hearted efforts to kill himself to avoid becoming Kotris which were prevented by a drone Kotris had sent, until the final confrontation between the two incarnations culminated in Straxus being exterminated as even the Daleks were disgusted with his selfishness. (AUDIO: ) When the Master made contact with the Cult of the Heretic and was offered an alliance with them if he killed one of his past selves - with the promise that the Cult would use the Anomaly Cage to prevent him being wiped out by the paradox - the Master laughed as he dismissed his past incarnations as foolish. Although he later claimed that he had targeted his past self at a point when he knew that the younger Master would survive, the two Masters found it difficult to cooperate, as the younger Master was more serious and dedicated to ensuring victory where the future Master's new lease on life had left him more inclined to make various bad jokes as he taunted his enemies. The older Master noted that the Cult's plans to remake the universe had been inspired by the beliefs of the renegade Time Lord known as the Heretic, whose belief that the universe was sick, led him to perceive regeneration as the only cure for this 'illness'. (AUDIO: )
Time Lords such as the War Chief were unconcerned about wasting regenerations, or Romana, who regenerated with no apparent need in order to assume an appearance she liked, (TV: , PROSE: ) while others such as the Doctor warned not to waste them. (PROSE: ) Iris Wildthyme once confided in Sam Jones that regeneration was treated on Gallifrey the same way sex was on Earth. (PROSE: )
In general, the Doctor avoided discussing regeneration with their companions unless someone else brought it up first, (TV: ) but explained the process in the aftermath. They were particularly open about the process in their eighth incarnation, telling companion Charley Pollard about regeneration and their past faces, noting at one point that he considered regeneration superior to the straightforward immortality of the ruthless Sebastian Grayle, as regeneration allowed him to change and develop as time went on where Grayle was stuck with one point of view and no real way to change. (AUDIO: ) Despite this, the Doctor's attitude towards regeneration seemed to change during their later incarnations, considering it more like true death. In their ninth incarnation, the Doctor bade farewell to his companion even though he was not actually dying. (TV: ) The Doctor's tenth incarnation was concerned about a prediction made regarding his own impending regeneration, saying, "Even if I change, it feels like dying. Everything I am dies. Some new man goes sauntering away...and I'm dead." (TV: ) Their tenth incarnation also compared regeneration to a lottery, in terms of what he becomes as a result of it; when meeting his immediate successor, he joked that his eleventh incarnation's bigger sonic screwdriver was "compensating". (TV: ) Following his regeneration into his seventh incarnation, the Doctor's memories of his sixth self's persona came to resent the current Doctor, accusing the current Doctor of "murdering" him (PROSE: ) before the Doctor came to accept that he was the Doctor in all his lives and forgive the sins of his previous self. (PROSE: ) The War Doctor, however, accepted the start of his regeneration, remarking that his old body was "wearing a bit thin" and even joking about his hopes for getting less-prominent ears. (TV: ) After receiving his new regeneration cycle, the Eleventh Doctor appeared relatively comfortable about his imminent regeneration, reflecting that everyone changed throughout their lives and the important thing was to remember who you had been, (TV: ) although his fear about the scale of the change he was about to experience prompted him to call his current companion in their personal future to ask her to stay with his next incarnation and help him through the transition to his new body. (TV: ) The Twelfth Doctor later recalled that the end of the First Doctor's life at Snowcap was "the place where [he] died", comparing it to Clara Oswald's limited memories of her 'splinters' by describing it as something so huge and terrible that the mind had to block it out in the aftermath. (COMIC: )
Despite his own attitude toward regeneration, both Harriet Jones (TV: ) and Sarah Jane Smith (TV: ) felt the same way about the Doctor throughout their incarnations. Harriet called the Tenth Doctor "absolutely the same man", still believing in this despite the Doctor threatening to destroy her government after she ordered Torchwood to blow up the Sycorax spaceship. (TV: , ) While the Brigadier noted that one Doctor was more than enough to deal with at any time, (TV: ) he nevertheless confidently proclaimed that all of the Doctors were "remarkable chaps", willing to work with whatever Doctor answered his calls for help even if he acknowledged that he knew certain Doctors better than others. (PROSE: ) Despite the importance of regeneration, the Doctor often failed to mention it to their companions, with the result that Ben, Polly, (TV: , ) Peri (TV: , ) and Rose (TV: , ) initially didn't believe that the new Doctor was the same person after their regeneration was complete. Even those companions who had been informed about the process in advance, such as Sarah Jane Smith, (TV: ) Adric, (TV: ) Melanie Bush (TV: ) and Clara Oswald, (TV: ) took a while to accept the new Doctor. Despite the close relationship between the Thirteenth Doctor and Yasmin Kahn, she ultimately chose to leave the Doctor when regeneration was imminent, each silently acknowledging that Yaz was so close to that particular incarnation that she would find it too difficult to spend time with the next one. (TV: )
After deciding to help the Doctor against the Mondasian Cybermen, the Missy incarnation of the Master was shown to see her past self as still being her, stating that she'd loved being him and the feeling of all that he was. However, due to her genuine desire to change, Missy mortally wounded her past self to force his regeneration into herself, appearing to see it as necessary to ensure the Master became Missy. (TV: )
=== Law ===
Former Lord Presidents were barred from serving another term in the same incarnation. As such, when Romana II decided to run again for the Presidency during the first months of the Last Great Time War, she promised to promptly regenerate if she received the public vote. However, she was instead defeated by Valerian. (AUDIO: )
== Regeneration in other species ==
Although most associated with Time Lords, regeneration also existed in other species, or sometimes in specific individuals, directly copied from the Time Lords.
=== Independent from Time Lords ===
The Kastrians, a silicon-based life form, were able to undergo an explicit process of regeneration, by absorbing radiation from the environment and/or in a dedicated "regeneration chamber" set with their specific genetic code. This form of regeneration was explicitly shown to allow a change in gender. (TV: )
Like their masters the Time Lords, the living timeships the TARDISes were capable of regenerating themselves if they were heavily damaged, leaving a very characteristic Artron energy trace when they did so. (COMIC: ) The Doctor's TARDIS was indeed returned to the Doctor with an altered outer plasmic shell and a changed console room on several occasions after breaking down and being engulfed in flames, often concurrently with the Doctor's own regeneration. (TV: , )
The Timeless Child was a member of a "Timeless" species with the power to regenerate an infinite number of times. This child's ability to regenerate was used by the Shobogan scientist Tecteun from Gallifrey to create the Time Lords. (TV: )
Kate Yates regenerated her hair when her Dalek Factor was activated after being hit by a car. (PROSE: )
=== Borrowed from the Time Lords ===
Swarm, an enemy of the Division and of the ancient versions of the Doctor who fought on the Division's behalf, showed the ability to renew himself after consuming the life force of Division agent En Sentac, reducing her to ash in the process. As he regenerated, Swarm glowed blue and red and the crystal growths on his face extended, before receding again as he settled into his new incarnation. (TV: )
Early in their history, the Time Lords discovered the planet Minyos, and gave the natives some of their technology. (TV: ) This included bestowing the power of regeneration on the Minyan royal family, who knew it as "cellular renewal", and kept it secret from their subjects until Oxirgi's revolution against the rule of the "Gods", during which the princess Malika faced public execution by firing squad and renewed herself in a flash of golden light immediately after she'd been shot. (COMIC: ) The crew of the Minyans' ship, the R1C, could regenerate indefinitely. Over time, they wearied of life. (TV: )
Time Lords fighting the War in Heaven gave the ability of regeneration to their lesser species regen-inf soldiers. (PROSE: , , ) Chris Cwej was regenerated by force to survive radiation poisoning. (PROSE: )
After the Toymaker, a Guardian of Time, merged with the Doctor's friend and fellow Time Lord Rallon, he gained a form of regeneration, albeit not in the direct way one might have expected. After centuries of keeping the Toymaker in check, Rallon 'died' when he triggered all twelve of his regenerations at once, but the Toymaker was subsequently kept in check by Rallon's Watcher, with the Doctor explaining the situation to his companions by using the analogy of the Toymaker having regenerated himself, the process causing some subtle changes in the . (PROSE: )
Mawdryn and his followers, who had stolen the Time Lords' regeneration technology, also had a great number of incarnations, though they had no control over when it would happen and what form, often grotesque, they would change into. Consequently, they longed for death, making their mutations a kind of de facto punishment by the Time Lords for stealing their technology. (TV: )
K9 Mark I, who had spent some time on Gallifrey, (TV: ) later regenerated by use of a regeneration unit emblazoned "∂³∑x²" after self-destructing to defeat a group of Jixen Warriors. (TV: ) He later regenerated again after exhausting his power core to defeat Trojan. (TV: )
During the Last Great Time War, the Daleks discovered the ability to use artron energy leeched from other time travellers to enact a similar renewal to the Time Lords'. This would allow the Dalek to repair its casing as well as heal its inner organic body. However, this process was still primitive by the time the destruction of Gallifrey by the Doctor; (PROSE: ) it also caused the Dalek to absorb DNA from the time traveller it had used to power its regeneration, beginning to mutate and deviated from the Dalek baseline. (TV: )
Due to being experimented on by the Dalek Overseer, an Ogron was sent to Gallifrey with the memories and certain biological traits of the Doctor, retaining DNA traces of the Doctor that created the impression that he was actually a regenerated Doctor rather than a completely different person. The Ogron, named "Doctor Ogron" by Bliss, was exterminated by the Daleks, but, due to possessing aspects of the Doctor's biology, regenerated. He was restored to life but did not change his appearance like a Time Lord would. (AUDIO: )
Davros, with the help of Colony Sarff, once tricked the Twelfth Doctor into sacrificing some regeneration energy to him and then funnelled much more energy than the Doctor had meant to give into the systems of the Dalek City, pumping all the dying Daleks there full of the regeneration energy. Lit aglow with the familiar orange halo, the Daleks emerged "renewed" and "more powerful", though this victory was short-lived, as, all according to the Doctor's plan, the mass of the regenerated Daleks in the sewers led to the destruction of the City. (TV: )
The CyberMasters, a group of Cybermen created by from the corpses of Time Lords, possessed the ability to regenerate due to their origins. (TV: )
== In other realities ==
In N-Space, at least, the changing of gender in regeneration was widely accepted as normal and a common occurrence. In at least one parallel universe, however, cross-gender regeneration could only be achieved by committing suicide; the Time Lords of this reality took a much dimmer view on the matter, considering it a criminal offence. (AUDIO: )
== Other references ==
The Aja'ib contained tales involving regeneration. (PROSE: Bafflement and Devotion)
== Behind the scenes ==
=== History of regeneration ===
==== Why regeneration? ====
Regeneration was introduced to the mythos of Doctor Who to solve a practical staffing problem: the production team needed to find a way to exit William Hartnell but still keep the show running.
The original idea for this replacement came from producer John Wiles and script editor Donald Tosh. They proposed to write out Hartnell during , a serial they commissioned and prepped, but ultimately didn't produce. Their notion was that the Toymaker would make the Hartnell Doctor disappear, but when the Doctor re-appeared he would magically be another actor entirely. (REF: The First Doctor Handbook, The Second Doctor Handbook) Though not at all a regenerative process as the term has since come to be understood, Wiles and Tosh do at least get some credit for being the first people to moot the possibility of carrying on the show with a new lead — and for the necessity of finding a narrative explanation for this switch. Though this is taken for granted today, this was an important milestone on the way to regeneration. Doctor Who could just as easily have gone down the route of another 1960s show, , where a main character was simply recast without narrative explanation.
However, Wiles and Tosh were ultimately unsuccessful in their bid to replace Hartnell, due to resistance from BBC Head of Serials, Gerald Savory. (REF: The Second Doctor Handbook) This failure was a part of the reason Wiles resigned relatively soon after taking over the show from Verity Lambert. (REF: The First Doctor Handbook)
His successor, Innes Lloyd, was better able to negotiate Hartnell's departure, in part because the climate within the BBC hierarchy had changed with Shaun Sutton's management elevation. (REF: The First Doctor Handbook) Still, it is uncertain who, precisely, came up with the idea of regeneration-as-biologic-process, rather than the mystical solution Wiles had earlier mooted. Howe, Stammers and Walker believed "the likelihood is that it emerged in discussion between Lloyd and his story editor Gerry Davis" — along with additional input from Shaun Sutton, and Kit Pedler. (REF: The Second Doctor Handbook)
==== Narrative origins ====
The earliest-known production office-generated document on the subject describes it thus:
Initially, the concept wasn't called "regeneration" at all, but rather "renewal". In fact, the term, so familiar to Doctor Who fans today, didn't appear until the Doctor's third regeneration, first seen by fans in 1974's . Since , Troughton's final story, merely had the Time Lords suggesting that they would "change [his] appearance", the only explanation of regeneration — for the show's first twelve years — was found in a cryptic exchange in part one of :
::Ben: Now look, the Doctor always wore this. So if you're him, it should fit now, shouldn't it?
:::Ben grabs the Doctor's hand and slips the signet ring on. But the ring, too big for the new Doctor's finger, falls to the TARDIS floor.
::Ben: There - that settles it.
::Doctor: I'd like to see a butterfly fit into a chrysalis case after it's spread its wings.
::Polly: Then you did change!
::Doctor: Life depends on change -- and renewal.
::Ben: (sarcastically) Oh so that's it. You've been renewed have ya?
::Doctor: (considering the notion seriously) I've been renewed, have I? That's it, I've been renewed! It's part of the TARDIS. Without it, I couldn't survive.
Although the Second Doctor's last claim of a connection between the TARDIS and regeneration has never been explored in detail, it is heavily suggested by later regeneration stories. Notably, the Third and Fourth Doctor's highest initial priority is returning to the TARDIS; (TV: , ) the Fifth Doctor desperately needs the TARDIS' Zero Room to assist with his regeneration; (TV: ) and the Eighth Doctor's post-regeneration amnesia is instantly resolved when Chang Lee opens the TARDIS' Eye of Harmony. (TV: ) The connection between man and vehicle was made explicitly clear by the visual effects in . There, the effect used for regenerative energy was the same as the energy that emanated from and was returned to, the heart of the TARDIS.
==== Tweaking regeneration ====
Beginning with the regeneration that resulted in the Fourth Doctor, each successive regeneration reveals a bit more about the mystery of the act.
 shows viewers that one Time Lord can help another by giving the process "a little push". This act of "gifting" regenerative energy is later expanded upon in Mawdryn Undead and . Both these stories take Cho-Je's "push" one step further by suggesting that regenerations can be outright gifted from one being to another.
The "Cho-Je push" is also tweaked a bit for the Doctor's fourth regeneration. In the audience is introduced to a kind of "mid-regeneration Doctor", a being called "the Watcher" who exists between the Fourth and Fifth Doctors. He then merges with the dying Fourth Doctor to start the regenerative process, and thus become the Fifth.
The notion that there is an existence for the Doctor within the act of regeneration is again mooted by the audio story Winter, which takes place almost entirely in that interim between incarnations. In Winter, the Doctor again merges with the Watcher to complete the transition into his next incarnation, though on this occasion the merging takes place inside the Doctor's mind between psychic recreations of both the Doctor and the echo of his future represented by the Watcher. Another "intra-regenerational" version of the Doctor is seen in The Trial of a Time Lord. The story's chief antagonist is implied to be the Doctor between his twelfth and thirteenth lives. A variation of this was seen in The Brink of Death, which depicts the Sixth Doctor in his mind at the moment of regeneration, including a brief moment where the Seventh Doctor 'speaks' to the Sixth before their voices merge as they state "It's far from being all over...", marking a successful regeneration.
Another novelty of the fourth regeneration is the introduction of the idea that a regeneration can "fail", resulting in the Doctor's death. (TV: ) But if the fourth regeneration focuses on a physical crisis, the next three surely stress the mental hardships of the act. The fifth regeneration leads to a kind of mania never before experienced by the Doctor. It even shakes loose some criminal tendencies. (TV: The Twin Dilemma) The next two regenerations cause temporary amnesia. (TV: , ) This condition is particularly profound in the newly arrived Eighth Doctor, who completely forgets all of his past history for a number of hours. Additionally, complications like amnesia can be brought on by anaesthesia, which holds chemical agents that interfere with regeneration. (TV: ) This regeneration also brings forth the notion that the Doctor actually dies prior to the metamorphosis of regeneration. The idea that the Doctor dies, even if briefly, is something that the Tenth Doctor later explains to Wilfred Mott in the first part of .
The tenth regeneration, whose after-effects are documented in , introduces the notion that the regenerative cycle lasts for fifteen hours. Within that window, the Doctor can lose body parts and yet re-grow them as he does with a hand he loses in battle with a Sycorax. Both Invasion and the preceding mini-episode also add another wrinkle to the mythos of regeneration. They show that the Doctor needs to expel regenerative energy in the aftermath of a change — something seen again in .
The Doctor's twelfth regeneration is shown to be tangibly explosive, something that hadn't been explored by any previous BBC Wales — or, for that matter, any — regeneration. That is, regenerative energy is depicted as being able to physically damage things. By the end of the cycle, the Doctor's TARDIS is itself in need of a "regeneration." It is implied that this explosive regeneration is due to the Doctor delaying it while he travelled to see all his former companions for an unknown period of time, thus allowing that regenerative energy to build up. (TV: , , )
Aspects of both the ninth and tenth regenerations are invested in River Song's second regeneration, as seen in . River Song practically begs to be shot by Nazi soldiers immediately after regeneration so that she can re-trigger her explosive regenerative energy and hurt them. The Hitler regeneration also definitively proves that skin colour can change through regeneration — though this had actually been practically settled long before by the "blue option" seen in Romana's Destiny of the Daleks regeneration.
The story featured what the Twelfth Doctor called "a state of grace", during which the regenerating Time Lord is restored to full health for a period of time, but grows steadily weaker and must decide whether or not to regenerate once it's over. This "state of grace" allowed an explanation for the Tenth Doctor's ability to delay regeneration to visit all of his former companions (TV: , ) and allowed for a story where the First Doctor and the Twelfth Doctor shared an adventure together that would help them determine whether or not they would regenerate or die.
==== Non-narrative explanations ====
Because of a relative lack of narrative explanation about regeneration, some writers of non-fictional or reference books about Doctor Who have tried to fill in the gap. One theory from such a source is that regeneration is caused by a "nanomolecular virus" that rebuilt the body much like the "self-replicating biogenic molecules". (REF: The Gallifrey Chronicles) This theory has not been repeated elsewhere, however.
==== That regenerative look ====
Each new regeneration was also radically different from the previous one, even in terms of the visual effects used to represent the moment of regeneration.
===== Do you remember the first time? =====
The very first regeneration was devised and executed by vision mixer Shirley Coward, who had rather unexpectedly come up with a method of achieving the effect electronically.
The original plan of the production team was simply that William Hartnell would fall to the floor at the end of and pull his cape over his face. Troughton would then appear at the beginning of , retracting the cloak. Coward's then-innovative vision mix necessitated that Troughton be hastily contracted for , part four. The series' first regeneration sequence was then duly recorded on 8 October 1966, with the cliffhanger resolution filmed two weeks later on 22 October. (REF: The Second Doctor Handbook)
The final episode of The Tenth Planet is missing from the BBC archives, however footage of the regeneration survives through a clip that was used on Blue Peter.
===== Regeneration recreation =====
As part of a missing episode, the Doctor's first regeneration has also been reconstructed four separate times:
* The first was for the DVD release of , where it was animated (along with the rest of Episode Four) by Planet 55.
* The second formed part of the climax for the TV biopic An Adventure in Space and Time - some of the specific shots leading up to the First Doctor's regeneration were recreated as part of the narrative showing Hartnell's final moments working on the show. The televised film did not feature the regeneration effect itself, however a recreation of the regeneration, featuring David Bradley as the First Doctor and Reese Shearsmith as the Second Doctor, was included as a bonus feature on the home video release.
* The third reconstruction served as a cold open for the animated reconstruction of in 2016. This version was touched up with minor improvements for a Special Edition release in 2020.
* The fourth and, to date, most recent recreation of the regeneration occurred for the TV story - shots of the First Doctor at the TARDIS console, as well as the First Doctor laying on the ground, were recreated with David Bradley in the role. This was followed with the original 1966 footage of Hartnell's Doctor regenerating into Troughton's.
===== Later regenerations =====
Each subsequent regeneration was then filmed in a variety of different ways, as dictated by the director on that particular episode. Indeed, no two regenerations were particularly similar until the first Russell T Davies era (2005-2010).
Only BBC Wales (and later BBC Studios Productions) Doctor Who attempted to standardise the way regeneration looked. With came what is now the standard "golden glow explosion" (although the colour of the explosion is fiery orange in and is milky white in , as well as rudimentary version of the effect appearing in TV: The Curse of Fatal Death). The subsequent Children in Need Special established that there was residual "regeneration energy" after a transformation which had to be expelled through the mouth. This was seen again in , and — though the latter narrative never made quite clear that Jenny had actually regenerated. Davies later gave the Restoration as a narrative explanation why the Doctor's regenerations are now golden in Doctor Who and the Time War.
This visual standardisation has allowed narratives to play around with regeneration. The mere presence of "regeneration energy" can now be used to heighten dramatic tension. This visual shortcut, unavailable to production teams in the classic era, has been a particular favourite of Steven Moffat, who used the "golden glow" liberally throughout the 2011 series; in fact, unlike in the first Russell T Davies era, in which nearly every regeneration had subtle differences, every Moffat era regeneration until TV: is nearly identical. Several of the 2011 episodes used that VFX in a way that wordlessly suggested regeneration. The effect shown in the last Twelfth Doctor and Steven Moffat story from Christmas 2017, and the fake-out regeneration seen in that year's uses closer visual language to the 2011 examples.
The transition at the end of 2022's (in broadcast terms part of the Chris Chibnall era but in production terms the beginning of the second Davies era filmed many months apart and involving two directors), notably had a significant change where the Doctor's clothing transformed once the Thirteenth Doctor regenerated into the Fourteenth Doctor. This had only happened before when the First Doctor's outfit changed into the Second Doctor's at the end of , when Innes Lloyd was the producer. The scene otherwise had a similar gold explosion effect to most previous regenerations. The first proper story of the second Davies era, 2023's , does not feature a regeneration per se, but the return of Donna Noble's memories and Donna and her daughter Rose "letting go" of the Human-Time Lord Meta-Crisis use the same shorthand of a golden glow around the characters to evoke regeneration energy, which is the term Fourteenth Doctor actor David Tennant and executive producer Phil Collinson directly refer to it as in the episode's in-vision commentary.
The standardised visual effects style carried into Staz Johnson's art for the 2017 comic story Doorway to Hell, which featured pre-Parting of the Ways and Utopia starting to regenerate. Colourist James Offredi also coloured the glow in golden shades similar to what was shown in either of the Russell T Davies eras, and the Steven Moffat and Chris Chibnall eras.
=== Fan fare ===
Fans have long speculated as to whether the Doctor could change sex or skin colour as a result of a regeneration. They've also long speculated on the number of times that a Time Lord can regenerate since both Doctor Who and The Sarah Jane Adventures have given different impressions on separate occasions.
==== Gender ====
It had long been "fanon" that regeneration can cause a change of gender in Time Lords. This theory was proven correct with the regenerations of several characters in the DWU, including the Doctor, whose thirteenth incarnation was a woman. Eldrad already displayed this change in The Hand of Fear and even stated that his species' regeneration process was the same as the one used by the Time Lords.
Female versions of the Doctor previously appeared in Comic Relief story The Curse of Fatal Death and in the Doctor Who Unbound story Exile, though the latter included rules and mindsets which do not exist in the prime Doctor Who universe.
In Interference - Book One and Book Two, the Time Lord I.M. Foreman was portrayed as having changed gender as a result of regeneration, though the character is noted as having received the gift of regeneration when the process was still experimental and unstable. A cut line in would have had Sneed remark to the Ninth Doctor, "I thought you'd be a woman," to which the Doctor would respond, "No, not yet." In Keeping up with the Joneses, the Tenth Doctor thought about the possibility of regenerating and acknowledged that it was "distantly possible" for him to regenerate into a woman. He thought this would "keep life interesting." In , the newly regenerated Doctor thinks for a short moment that he is a girl.
In , the Doctor mentions the Corsair, who has regenerated into both male and female incarnations. Similarly, Harvest of Time revealed that one of 's potential future incarnations was female; a female Master going by the name Missy later appeared in . had the Sisterhood of Karn boast that they could control regeneration and give the Eighth Doctor the choice of "man or woman" for his next incarnation. showed the first on-screen male-to-female regeneration with the General's eleventh regeneration, shortly after The Black Hole had featured the first one ever. The General's first nine incarnations were female and she was pleased to return to a female incarnation. The Gallifrey series later depicted the first female-to-male regeneration through Trave's regeneration in Enemy Lines. The Twelfth Doctor's regeneration finally resulted in him becoming a woman, in 2017's .
==== Skin colour ====
In The Sarah Jane Adventures story the Eleventh Doctor noted that his racial characteristics were not limited to white; he "can be anything". Although both actors to play K'anpo Rimpoche were Caucasian, Kevin Lindsay donned an accent and was made up to appear ethnically Tibetan. (TV: ) Romana was seen to regenerate into a blue-skinned form in TV: Destiny of the Daleks. Rassilon has been portrayed by white actors Richard Mathews, Timothy Dalton and Donald Sumpter on-screen while black actor Don Warrington was Rassilon's voice actor and cover-art model in Big Finish Doctor Who audio stories. In , River Song's second incarnation was black, while her first (in / and ) and third and last (appearing throughout series 4, 5, 6, 7, and 9) were white. Further, the General's eleventh regeneration was from a white man into a black woman. (TV: ) One of Rindle's incarnations had darker skin than several previous incarnations. (AUDIO: The Lady in the Lake) Karlax regenerated into a body that had darker coloured skin than his previous body. (PROSE: Engines of War).
==== Number ====
Russell T Davies noted how firmly the concept of limiting Time Lords to thirteen lives, introduced in The Deadly Assassin, was lodged in fans' minds. Davies attempted to deliberately subvert the limit in , though he admits that the fandom may resist his attempt to alter the programme's mythos.
However, events depicted in Steven Moffat's confirm the twelve-regeneration limit for Time Lords, and of the Doctor in particular, with the events of Time exploring the impact this has on the character having finally reached his limit, the Doctor facing his final death of old age until the Time Lords send him the energy for a new regeneration cycle. Several characters express a lack of knowledge over how many regenerations the Doctor currently has including the Doctor himself, (TV: ) Rassilon who had a hand in giving him the new regeneration cycle (TV: ) and the Master. (TV: ) Currently, a number has never been given for the number of regenerations the Doctor possesses in this second cycle. It is also unclear if the portion of regeneration energy that was stolen from the Twelfth Doctor by Davros impacted his ability to regenerate in any way. (TV: ) The number of possible future regenerations came into more dispute with the release of , which revealed the Doctor to be of a species with seemingly unlimited regenerations. It has not since been made clear if they retain this ability, or if they are still bound by the usual Time Lord limitations.
== Footnotes ==
cs:Regenerace
de:Regeneration
es:Regeneración
fr:Régénération
pt:Regeneração
ro:Regenerare
 
Category:Time Lord abilities
Category:Longevity and ageing
Category:Apparent death
Category:Gallifreyan history
Category:Magic