Fourth Doctor

The Fourth Doctor is the fourth incarnation of the Doctor to appear in Doctor Who and the main protagonist of Seasons 12 to 18. 
He is portrayed by .
==Biography==
The Fourth Doctor regenerated from the Third Doctor following his encounter with the "Great One" of the Eight Legs. The Doctor was left delirious after the regeneration and Medical Officer Harry Sullivan was left to deal with him. The Doctor was far more eager to abandon UNIT, but was convinced by Sarah Jane Smith and the Brigadier to aid them in investigating Think Tank. The Doctor, Sarah and Harry managed to defeat the Scientific Reform Society, and the Doctor managed to destroy their out of control K1 robot with a metal virus. Afterwards, the Doctor convinced Sarah Jane to rejoin him in exploring the cosmos, with them taking on Harry Sullivan as a travelling companion. 
=== Round trip to Nerva ===
Harry accidentally brought them to the space station Nerva, and they managed to save the humans from the Wirrn. Beaming down to Earth, the Doctor that the Sontaran Styre conducting experiments on humans as a prelude to an invasion. The Doctor challenged him to a duel and while he was beaten by the Field Major, this was a trap for the exhausted Styre. Harry had damaged his ship so that his re-energising process would be reversed, and the Doctor bluffed the Sontaran Marshall into calling off his attack. 
While intending to return to Nerva and the TARDIS, in Genesis of the Daleks the Doctor was forcibly enlisted by the Time Lords to travel back in time and prevent the genesis of the Daleks on Skaro. Upon their arrival on Skaro, the Doctor, Sarah Jane and Harry was caught up in a war between the Kaleds and Thals, with the Doctor being taken prisoner by the Kaleds with Harry after being separated from Sarah Jane. In doing so, the Doctor encountered the Daleks' creator, the psychopathic Kaled scientist Davros, who designed the Dalek casings to be containers for the Kaleds' final evolution. The Doctor tried and failed to convince Davros to alter the Dalek's development. After rescuing Sarah from the Thals, the Doctor discovered Davros playing both sides, and wound being captured, thinking Sarah and Harry had been killed in the final assault on the Kaleds city. 
Being let go with the war's end, the Doctor and the Thal Bettan were shocked to find the Daleks retribution against the Thals, and she helped him escape. Reuniting with Sarah and Harry they confronted Davros, who interrogated the Doctor on the Dalek's future history, and how to avoid their defeats. The Doctor posed the question of what Davros would do with a hypothetical virus that could wipe out all life. When Davros revealed he would use such power, the horrified Doctor attempted to force him into stopping the Daleks, but was prevented. Although the Doctor eventually found himself in a position to destroy the Daleks, he ultimately decided he did not have the right. Afterwards, the Doctor destroyed Davros' recording of the future. While he attempted to prevent their rise to power, Davros outplayed the remaining Kaleds, and the Doctor ended up tricking a Dalek into destroying their incubation chamber. As the Daleks turned on Davros, the Doctor and the Thals managed to bury them underground, slowing down their development by a thousand years. 
Shortly after in Revenge of the Cybermen, the trio arrived at Nerva in it's past as a space beacon, and found the majority of it's crew killed by a plague. The Doctor worked out that this was an artificial plague being spread by a Cybermat on behalf of the Cybermen. After Sarah was infected, the Doctor was forced to beam Sarah and Harry to Voga. The Doctor found that the Cybermen planned to destroy the remnants of Voga and it's people, and along with the crew, was forcibly strapped with an explosive. However, Harry clumisly rescued the Doctor and he and Sarah managed to prevent the Cybermen's back up plan of smashing the beacon into the planet. 
=== Season 13 ===
After aiding UNIT in defeating the Zygons, the Doctor was eager to abandon his ties with Earth. The Doctor and Sarah were drawn to a distress call 30'000 years in the future, where he prevented anti-matter being taken from Zeta Minor. Soon after in 1911, the Doctor and Sarah were drawn into one of their greatest battles, to prevent Sutekh the Destroyer from freeing himself via his servants, namely his robotic mummies and the possessed Marcus Scarman. The Doctor was far more sombre in response to this grave threat, even taking Sarah to a destroyed version of her home time to underline the danger the Osirian posed. While they managed to destroy a rocket intended to destroy the Eye of Horus, the Doctor was captured by Sutekh and put under his control. After taking them to Mars, the Doctor was freed after he was unsuccessfully killed. Though unable to stop Scarman from releasing him, the Doctor was able to delay Sutekh's trip through a time corridor by entrapping him within for eternity. 
=== The Deadly Assassin ===
The Fourth Doctor would later be summoned to Gallifrey and, unable to take Sarah Jane with him, was forced to say goodbye to her, bringing her back to Earth before he departed. On Gallifrey, the Doctor found he had been framed for the murder of the Lord President and, to avoid being sentenced to death, invoked Article 17 of the Time Lord Constitution to run for President, with his opponent being Chancellor Goth. Eventually, the true culprit behind the assassination was exposed as Goth himself, who had acted due to influence of the decaying Master. As a result, the Fourth Doctor became President of Gallifrey by default, but ultimately chose to continue his adventures in outer space instead rather than rule over Gallifrey, leading Borusa to become Acting President in his place.
After resuming his adventures, the Doctor quickly received a new companion in the form of Leela of the Sevateem, and later on was joined by the dog-like robot K9.
=== The Invasion of Time ===
The Doctor would later return to Gallifrey in response to the Vardans' invasion of the planet and assume the mantle of Lord President to investigate the true culprit behind the invasion, which turned out to be the Sontarans. After the Doctor thwarted the invasion, he found himself bidding farewell to Leela after she chose to stay behind on Gallifrey, having fallen in love with the Time Lord Andred.
=== The Key to Time ===
For his next adventure, the Doctor found himself partnered with fellow Time Lord Romana as the two were enlisted by the White Guardian to seek out all five pieces to the Key to Time in order to stop his evil counterpart, the Black Guardian. After defeating the Black Guardian, the Doctor resumed his regular adventures with Romana at his side, with a randomiser installed to prevent him being able to find them. 
=== Destiny of the Daleks ===
One outing saw the Doctor and a newly regenerated Romana finding themselves in the middle of the war between the Daleks and the Movellans, in which the Doctor once again encountered Davros, who had survived his supposed demise and been excavated by his creations.
=== Nearing the end ===
When he felt his regeneration nearing, the Doctor became more sombre and weary at the universe, changing his clothes into a macabre burgundy. The Doctor's adventures later led him to being joined by the E-Space youth Adric and eventually brought him to Traken, where he became entangled in another plot by the decaying Master, who sought to steal the body of the Traken keeper Tremas, whose daughter Nyssa would go on to join the Doctor as a companion. While he managed to prevent the Master stealing the Souce, unbeknownst to him, the Master managed to steal a new body for himself and emerging in a new, more unhinged incarnation.
==== Logopolis ====
While attempting to repair the TARDIS's Chameleon Circuit, The Doctor encountered the new Master, and was haunted by the ghostly Watcher, who was a premonition of the future. While journeying to Logopolis, the Doctor was joined by Tegan Jovanka, who joined him by accident, as well as Nyssa, and he found the Master interfering with their calculations. The Master's actions resulted in entropy entering the universe, and the Doctor was forced to work with him to open a CVE to prevent the universe becoming undone. At Pharos Tower, the Master double-crossed him and the following struggle led to the universe being saved, but the Dctor was fatally wounded. In the end, the Watcher merged with him, leading him to regenerate into the Fifth Doctor.
=== Legacy ===
At some point, a future incarnation of the Doctor would "revisit" the face of the Fourth Doctor and become curator of the Under Gallery.
==Personality==
The Fourth Doctor was much more eccentric than his previous incarnations, dressing oddly and delighting in pulling pranks and making odd jokes. He also had a stronger anti-authoritarian streak, which led him to depart from UNIT and travel through space with only his companions, as well as trying to avoid the politics of the Time Lords whenever possible. Despite his goofy demeanor, this Doctor was still highly intelligent and cunning, and had a serious side that he occasionally showed in dire situations.
==Quotes==
==Trivia==
*The Fourth Doctor is less scatterbrained and more using the facade of being so after Sarah Jane left his company; allowing him to have an undisclosed amount of time to mellow.
**Kimpo Ropochei did mention forcing a regeneration on the freshly deceased Third Doctor to bring him back to life would scramble the next Doctor's brain.
*The Fourth Doctor has the longest TV tenure out of any Doctor, with Tom Baker portraying him for seven years.
*Tom Baker had undiagnosed bipolar disorder, which led him to become highly immersed in the role of the Fourth Doctor and very protective of the character. As a result, after leaving Doctor Who, Tom Baker stayed away from the show for a period of time to focus on his mental health, declining a chance to return for the "The Five Doctors" special. Because of this, the Fourth Doctor was portrayed in the special through the use of archival footage.
**Fans of the Revived Series hoped someone would break the record, but none of the Doctors from 9 through 14 have manages to stay more than three seasons.
*The Nest Cottage Chronicles audio series was the first time Tom Baker reprised the role of the Doctor in the 2st century. It's writer Paul Magrs intended to be interpreted as both part of the mainstream Fourth Doctor's adventures, and feature a version outside of th TV continuity. 
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