K9 K9 — occasionally written as K - 9 or K • 9 — was the designation given to a series of intelligent , dog - like robot s who served as companions of Professor Marius , the Fourth Doctor , Leela , Romana , the Mistress , Sarah Jane Smith , Luke Smith , Starkey , and the Tenth Doctor . K9 Mark I , II , III , and IV addressed whoever was directing them as " Master " or " Mistress " depending upon gender , and used the formal " affirmative " and " negative " rather than " yes " and " no " . They were programmed to be both loyal and logical , with a penchant for taking orders literally , almost to a fault . Their striped collars mirrored the Fourth Doctor ' s trademark scarf . Biography . K9 Mark I . Professor Frederick Marius , who invented the first K9 in the year 5000 while working on the asteroid K4067 , described him as " my best friend and constant companion . " Marius had a dog on Earth , but weight requirements did not allow him to bring his real dog into space , so he built K9 . ( TV : " The Invisible Enemy " ) He built K9 by using the latest technology . Marius used his own medical computer , a state - of - the - art intraresponsive brain app , protective anti - radiation cladding , probes , a laser scapel , a vision and voice box and two scanning antennas . He put these parts together and created K9 . ( PROSE : " One Man and His Dog " ) According to one account , the Professor copied the remnants of one of the versions of K9 created by the Doctor and given to Sarah Jane Smith . ( PROSE : " Tautology " ) The Professor offered K9 to the Fourth Doctor as the same weight requirements made him unable to take Mark I back to Earth . ( TV : " The Invisible Enemy " ) After adventures with Leela and the Doctor , Mark I decided to stay on Gallifrey with his " mistress " . ( TV : " The Invasion of Time " ) . The Fourth Doctor and K9 Mark II spent an indeterminate period of time together . However , the Doctor appeared to be activating K9 Mark II , implying that no significant time had elapsed since leaving Gallifrey . ( TV : " The Ribos Operation " ) It is possible that the Doctor spent some time at Nest Cottage before activating him . ( AUDIO : " The Stuff of Nightmares " ) There are accounts that this model of K9 went on missions on behalf of the Time Lord s and was given control of a space vessel called " K - NEL " . ( " K9 and the Time Trap " , et al ) K9 stayed with Leela on Gallifrey for many years . It was only after the disappearance of her Time Lord husband , Andred , that Leela and her K9 met Romana II and " her " K9 . The two K9s did not get on well and competed . ( AUDIO : " Weapon of Choice " ) After Leela became Romana ' s bodyguard and after many important missions on her behalf , Leela ' s K9 was destroyed by an exploding bomb . Leela was heartbroken , but refused to have a duplicate unit built . ( AUDIO : " Imperiatrix " ) However , K9 survived this and the Last Great Time War . He witnessed the murder of Zanthus Pia by Ahab . His Jixen henchmen fought him and were transported to 2050 Earth . K9 self - destructed to protect the humans nearby , then regenerated into a more advanced model . ( TV : " Regeneration " , " The Bounty Hunter " ) K9 Mark II . Before this , the Doctor obtained or constructed at least one backup model of K9 . Immediately after leaving Mark I behind with Leela , he unpacked K9 Mark II . This version of K9 accompanied the Doctor and his new companion on their quest to locate the segments of the Key to Time , ( TV : " The Ribos Operation " ) but the swampy terrain of Delta III made it impossible for him to join them on the planet . At the conclusion of the quest , the Shadow turned K9 to his evil will , giving K9 a sinister personality . ( TV : " The Armageddon Factor " ) The Fourth Doctor found that K9 had contracted laryngitis and had lost his voice as a result of this . K9 was left in the TARDIS while the Doctor and Romana II battled the Dalek s and Davros . ( TV : " Destiny of the Daleks " ) During a later adventure , he remained patiently in the TARDIS , which would imply that his voice had not yet returned . ( TV : " City of Death " ) After his voice returned , it sounded quite different and remained so for a while ( TV : " The Creature from the Pit " ) before the familiar voice returned . ( TV : " The Leisure Hive " ) This K9 exhibited the ability to sense and warn others of danger . He was also more mobile than his predecessor , despite his problems with the swamps of Delta III . ( TV : " The Armageddon Factor " ) The Doctor often used a glib remark to disarm those who were surprised by K9 ' s appearance , such as " They ' re all the rage in Trenton , New Jersey . " ( TV : " The Stones of Blood " ) K9 travelled to E - Space with the Fourth Doctor and Romana II , where they met Adric . He had his head knocked off while trying to defend Romana , Adric , Varsh , Tylos and Keera . ( TV : " Full Circle " ) Damaged by the time winds , K9 Mark II could not cross back into N - Space with the Doctor . He decided to stay behind at the Gateway with Romana II to help her free the remaining Tharils from slavery . ( TV : " Warriors ' Gate " ) Eventually , Romana II and the presumably repaired K9 returned to their own universe and K9 Mark II came to live on Gallifrey . ( PROSE : " Lungbarrow " , WC : " Shada " , AUDIO : " Zagreus " ) During Romana ' s Presidency of Gallifrey , Leela became her bodyguard , and the two K9 units were forced to work together , not always amicably . After Matthias had replaced Romana as President , he nominated her to undertake a mission to find a cure for the Free Time virus , to be followed by exile . K9 opted to remain in the employ of Matthias , fighting the infection on Gallifrey . However , Braxiatel and K9 had planned another operation . Realising that the only cure to the virus was to end the regeneration capabilities of the Time Lords , Braxiatel used a Time Scoop to collect the Time Lord bio - data archive ( along with K9 ) . Romana was asked to decide whether to administer the cure or let Gallifrey die and rebuild it from scratch with the bio - data archive . ( AUDIO : " Gallifrey " ) K9 Mark III . A third model , K9 Mark III ( again either obtained or constructed by the Doctor ) was shipped in 1978 to Sarah Jane Smith at the home she had shared with her Aunt Lavinia in South Croydon during her companionship of the Third and Fourth Doctors . ( TV : " A Girl ' s Best Friend " ) Since parting ways with the Doctor ( TV : " The Hand of Fear " ) however , Sarah Jane had already gone away and was travelling extensively . The following year , Lavinia purchased a manor house and market garden in Moreton Harwood , Gloucester , and took the still crated K9 with her . On 18 December 1981 , Sarah Jane and her foster brother Brendan Richards arrived at Lavinia ' s home for Christmas , but Lavinia had left early for her lecture series in the United States . Sarah Jane opened the crate and received her new companion . ( TV : " A Girl ' s Best Friend " ) K9 helped Sarah Jane to defeat Moreton Harwood ' s murderous Hecate Cult . ( TV : " A Girl ' s Best Friend " ) " Circa " 1983 , K9 Mark III and Sarah Jane lived in semi - detached house where their gate bore a " beware of dog " sign and Sarah Jane permitted him outside unconcealed . Sensing danger , he advised Sarah Jane to either not go out , or to take him with her . She declined , and K9 thus did not accompany her to Gallifrey . ( TV : " The Five Doctors " ) K9 accompanied Sarah to an archaeological dig in Egypt . ( COMIC : " City of Devils " ) In the early 1990s , K9 assisted Sarah in investigating a supposedly haunted house . ( PROSE : " Housewarming " ) In 1996 , Sarah used K9 to hack into records and find Sam Jones ' home address and later to translate Lost Boy ' s speech . ( PROSE : " Interference - Book One " ) K9 was briefly possessed by a malevolent entity , but was freed when Sarah accidentally electrocuted him . ( PROSE : " The Sow in Rut " ) K9 began slowly breaking down and eventually ended up deactivated in a cardboard box in Sarah ' s attic . ( PROSE : " Moving On " ) Hilda Winters had K9 dismantled and analysed . ( AUDIO : " Mirror , Signal , Manoeuvre " ) In early 2007 , K9 was reactivated by the Tenth Doctor ; Sarah Jane was unable to go to any humans for repairs prior as the parts inside K9 could change history . K9 ' s repairs were short lived . In battling Lucas Finch and his Krillitane invasion at the school the next day , Mark III blew up a vat of Krillitane oil , which was now lethal to the Krillitanes destroying himself and the Krillitanes in the process . ( TV : " School Reunion " ) K9 Mark IV . As a heartbroken Sarah Jane watched the Tenth Doctor depart , the TARDIS dematerialised to reveal Mark IV . K9 said the Doctor rebuilt him with " new omniflexible hyperlink capabilities " . ( TV : " School Reunion " ) Almost as soon as he arrived , K9 Mark IV left Sarah Jane to stabilise a dangerous black hole in space which had been created in Switzerland . He could only speak with Sarah Jane occasionally via a cabinet with a space - time link when the orbit of the black hole intersected with Earth ' s and did not know when he would complete the job . ( TV : " Invasion of the Bane " ) However , he returned to Earth very briefly during emergencies . He did so on two later occasions in order to render vital assistance . The first time , he fought Mr Smith in pitched battle to give Sarah Jane time to upload the Armageddon Virus . ( TV : " The Lost Boy " ) The second time , he quickly uploaded TARDIS base codes to Mr Smith , assisting the Tenth Doctor in returning Earth to its correct location in space . ( TV : " Journey ' s End " ) After these events , he returned to monitoring the black hole . He emerged to find a member of the Slitheen family attempting to steal him as part of a revenge plot against Sarah Jane , as she had foiled their plans in the past . K9 banished the Slitheen after reversing one of its attacks . ( TV : " From Raxacoricofallapatorius With Love " ) K9 returned when Ship used the black hole as fuel . Though Sarah Jane , Luke , Rani and Clyde were happy to have K9 back , Mr Smith was not . ( TV : " The Mad Woman in the Attic " ) K9 spent a lot of his time in Sarah Jane ' s attic at 13 Bannerman Road , Ealing , but left to defeat Travast Polong . He attended Sarah Jane ' s abortive wedding to Peter Dalton , where he helped the Tenth Doctor , Luke , Rani and Clyde defeat the Trickster . ( TV : " The Wedding of Sarah Jane Smith " ) After helping defeat the Slitheen family , Clyde brought K9 to Park Vale Comprehensive School to help him with his test . He helped defeat the Rakweed before returning home . ( TV : " The Gift " ) K9 went to the University of Oxford with Luke , but restored Mr White ' s original programming through a mobile phone . ( TV : " Goodbye , Sarah Jane Smith " ) Unlike 25 years earlier where she appeared unconcerned with K9 Mark III being seen , Sarah Jane restricted K9 Mark IV to her Ealing house except in emergencies or when she required his services , lest she have to explain him . Her son Luke covered by explaining to a puzzled Peter Dalton that K9 was a Japanese robot toy with pre - programmed phrases . ( TV : " The Wedding of Sarah Jane Smith " ) Nevertheless , she sent K9 to serve Luke when he went away to the University of Oxford . ( TV : " The Nightmare Man " ) Whereas Sarah Jane lifted K9 Mark III into and out of her car , ( TV : " A Girl ' s Best Friend " ) K9 Mark IV had a " hover mode " allowing him to negotiate the stairs of the Smiths ' three - story house and bi - level attic , and to enter and exit cars . ( TV : " The Wedding of Sarah Jane Smith " , " The Gift " ) The Eleventh Doctor implied that Mark IV was not the first to have the ability to hover . ( TV : " The Power of Three " ) Living art simulation . During an encounter with the sentient painting , the " Mona Lisa " at the International Gallery , a simulation of K9 Mk IV was created when Mona Lisa was tricked into animating a drawing of K9 made by Clyde inside a cloud of mystic drawing - animation energy . He subsequently defeated " The Abomination " , another evil painting - come - to - life , before disappearing as the Mona Lisa herself reverted to being an immobile painting . ( TV : " Mona Lisa ' s Revenge " ) Tenth Doctor ' s Model . During his travels with Rose Tyler , the Doctor built a model which mainly stayed in the TARDIS as a pet . ( COMIC : " Untitled " ) This model was in the ship long after both Rose and Martha left , and was heavily present during the Doctor ' s downtime with Rose - the - Cat . Rose enjoyed making fun of K9 . ( COMIC : " A Rose by Any Other Name " ) K9 Mark 2 . After Mark I sacrificed himself to destroy the Jixen warriors , Starkey retrieved his regeneration unit . K9 was rebuilt as a much more advanced model , but had no memories . He stayed at the house of Alistair Gryffen , who ran tests on K9 , but did not tell the Department . K9 tried to kill Starkey , as he was sprayed with Jixen genetic matter and so registered as a Jixen . Starkey convinced him that he was not an enemy and K9 gave him his dog whistle to summon him when needed . ( TV : " Regeneration " ) K9 and the team tracked down the surviving Jixen to Dauntless Prison and killed it . They also faced a Meron and freed the alien prisoners . ( TV : " Liberation " ) K9 travelled with Starkey when he was on the run from the Department and rescued Gryffen ( who was kidnapped by a Korven ) . Gryffen later welcomed him and Starkey into his home . ( TV : " The Korven " ) Later he defeated Ahab , who tried to convince him he had murdered Zanthus Pia . He became part of the K9 Unit , being made the responsibility of Gryffen and under the control of Department inspector June Turner . ( TV : " The Bounty Hunter " ) He foiled Inspector Drake ' s plan to control the population using Cerulium ( TV : " Sirens of Ceres " ) and experienced fear . ( TV : " Fear Itself " ) He aided in the defeat of echoes of Gryffen ' s family , ( TV : " The Fall of the House of Gryffen " ) Orthrus , a duplicate of him created by Drake to frame him ( TV : " Jaws of Orthrus " ) and the Bodach . ( TV : " Dream - Eaters " ) He met Nehetka and Geb of the Anubian s , a race his previous incarnation liberated . He was so obsessed with regaining his lost memories that he didn ' t notice Gryffen , Starkey and Jorjie ' s takeover by the Anubians . He soon found out when the Anubians attacked the Department . With Darius ' help , he defeated them . ( TV : " Curse of Anubis " ) He helped Starkey fight the Oroborus , ( TV : " Oroborus " ) free the Mede s ( TV : " Alien Avatar " ) and help one of the last Aeolian s find her mate . ( TV : " Aeolian " ) He saved a Centuripede and her young from being killed by Drake ( TV : " The Last Oak Tree " ) and absorbed the Hunger swarm which threatened to devour Earth . ( TV : " Black Hunger " ) He and Starkey went through the STM to 1963 , where they rescued Jorjie and saved Darius ' great - grandfather William Pike from arrest and Darius from erasure from history . ( TV : " The Cambridge Spy " ) He enlisted the help of the Ukkan librarian Yssaringintinka to rescue Starkey , trapped on the planet Urlic . ( TV : " Lost Library of Ukko " ) He helped Birdie , a CCPC whith implanted human DNA , escape from the Department . ( TV : " Mutant Copper " ) He discovered the last of the Etydion s ( TV : " The Custodians " ) and taught Taphony how to be a friend . ( TV : " Taphony and the Time Loop " ) Either Inspector Thorne or Lomax found out about K9 ' s regeneration unit and decided to acquire it . Thorne joined forces with Freddie Maxwell , owner of Crashclub involving old robots being made to fight . K9 went undercover as a gladiator and made friends with the robot clowns Chuckles and Boris . He was called to fight the Pain - Maker , who was laced with the explosive solarmite . When he was set to self - destruct , K9 detected this and fled the explosion . ( TV : " Robot Gladiators " ) To regain his memory and find out his connection to the STM , K9 ' s archive was scrambled . Directives from the STM almost caused him to self - destruct and lose all his memory . However , with Gryffen and Starkey ' s help he overrode the directives . ( TV : " Mind Snap " ) He helped Gryffen find the STM ' s temporal stabiliser from the fallen angel crash site in Canada , where it was revealed to be Korven technology . ( TV : " Angel of the North " ) He stopped haywire CCPCs when The Last Precinct ' s plan backfired . ( TV : " The Last Precinct " ) After this he was tricked by Thorne to give him his regeneration unit for a lost memory chip . This turned him into a bomb to make him self - destruct on encountering Jixey . Starkey helped him disarm himself . ( TV : " Hound of the Korven " ) K9 Mark 2 ' s brief life was almost cut tragically short when after the fall of the Korven invasion force , Thorne sent the Trojan to kill K9 , who defeated it by burning out his power core and exhausting all his energy . As his regeneration unit was in the Trojan , K9 seemingly died at the mansion after his companions bade him farewell . However his regeneration unit homed in at the last minute and resurrected him , giving the frisky pup a new lease on life . The regeneration unit restored his old dog collar so he could celebrate the joyful occasion to the full as he flew off to more adventures , bristling with life . ( TV : " The Eclipse of the Korven " ) Someday K9 saved the people at the Aurora from being killed by a Federation war cruiser . ( PROSE : " Peaceniks " ) When K9 wanted to help a space ship navigating back to New Earth he met Interstitials . These creatures were living in a state relating to the space or time between things . K9 helped them pass into another existence where it was better for them . ( PROSE : " Interstitials " ) When being imprisoned by the Sporraxx they tried to access K9 ' s memory core . Memories that K9 had assumed to be erased were slowly coming back and the Sporraxx got to know more and more about K9 ' s past . They reprogrammed K9 to protect a small spherical marauder bomb , that would destroy Earth . However K9 was able to break free of their control , because deep in his memories a sense of right and wrong prevailed . He took the bomb back into the Sporraxx space ship where it exploded . ( COMIC : " Short Circuit " ) 10800 years after the Punch and Judy shows were created and performed by ltinerant children entertainers , K9 was hired by Professor Peabody to protect her son Lukran Peabody . Lukran got kidnapped by the Pyxian s but was saved by K9 who returned Lurkan to his mother and stopped the Pyxians . ( PROSE : " Stranger On The Train " ) Future models . According to Braxiatel , Bernice Summerfield gave him a K9 model at some point . ( AUDIO : " Weapon of Choice " ) However , Brax was an almost habitual liar , and no definitive account of this act of generosity was known to exist . Personality . K9 had a personality very consistent across the models with some contact with the Doctor . He was polite and formal , with pedantry bordering on condescension . Though he often displayed feelings such as sorrow ( TV : " The Invasion of Time " ) and self - regard ( TV : " School Reunion " ) , he often stated that he had not been programmed to have emotions . ( TV : " Invasion of the Bane " ) He did not use contractions such as " you ' ve " for " you have " and addressed others by titles such as " Master " , " Mistress " , " Doctor - Master " ( to refer to the Doctor ) or " Young Master " ( Adric , Starkey and in one instance , Clyde ) . Though he did not seem to resent his subordinate status , he sided with the Doctor ' s companions over the Doctor and showed a dark side , regarding other artificial intelligences with contempt . ( TV : " The Invasion of Time " , TV : " The Wedding of Sarah Jane Smith " , TV : " Robot Gladiators " ) He relished a brief chance to act as a figure of power . ( PROSE : " The Well - Mannered War " ) He usually did not engage in computer - like literal thinking , though on one occasion he followed Romana ' s instructions to " forget it " to the letter and erased all knowledge of tennis from his memory banks . ( TV : " The Stones of Blood " ) With his great intelligence , he had a tendency to bore people with facts and did not stop immediately when asked , as he did to Leela on Pluto . When being told that he would have to stay behind in the TARDIS , K9 often argued , giving the Doctor reasons why he should go such as " he would be a good dog . " K9 always wanted to assist the Doctor . He had great intelligence and skill at chess , claiming to be able to beat the Doctor in six moves ( although this may only have been because he was programmed with all chess games since 1886 ) . ( TV : " The Sun Makers " , " The Androids of Tara " ) K9 had an aggression mode . ( TV : " State of Decay " ) K9 Mark 2 had some obvious commonalities with the Mark I that had preceded him . However , as he had almost completely lost his " personal " memories , he was forced to reacquaint himself with the world around him . Toward this end , he downloaded thousands of human movies onto his memdrive , which peppered his speech with 20th and 21st century English colloquialisms that his " brothers " did not typically employ . ( TV : " Alien Avatar " ) Despite his negative opinions of emotions , ( TV : " Mutant Copper " ) he asked questions about some , such as fear ( TV : " Fear Itself " ) and love ( TV : " Aeolian " ) . He even showed some , laughing when he saved the day , feeling fear ( TV : " Fear Itself " ) and being angry . ( TV : " Regeneration " ) Features . K9 Mark I ' s mechanisms included rotating ear - probes , telescopic " eye " probe , an extendable nose concealing a powerful laser weapon , flashing lights on the top and the " eye " panel , waggling tail antennae , and ticker - tape tongue . His head could move up and down . His shell was painted in metallic gold / grey . There was a monitor screen on his left flank , though K9 rarely used this during his travels with the Doctor . Around K9 ' s neck was a tartan collar , ( being the Family Tartan of the Clan Buchanonn ) from which hung a silver disk . ( TV : " The Invisible Enemy " ) He was later modified to fly through the vacuum of space . ( TV : " Curse of Anubis " ) After K9 Mark I was left behind with Leela on Gallifrey , the Doctor had K9 Mark II in a box in storage . ( TV : " The Invasion of Time " ) In addition to minor cosmetic alterations on the previous model ( including the new metallic charcoal paint - work ) , K9 Mark II also had a slightly different character from his predecessor . Gone was the product of Marius ' version ' s 5000 AD technology . This new K9 was a product of the Doctor ' s own technology and values . The gun was now used for stunning , not killing and he responded to a dog - whistle . When the Doctor left Sarah Jane Smith on Earth , he created K9 Mark III as Sarah ' s companion . The new mechanics of K9 Mark III included larger wheels and a front and back - wheel drive . K9 was also given a brand new coat of paint ( this time a metallic blue ) and a handle on top of his shell to make carrying him easier . ( TV : " A Girl ' s Best Friend " ) When the Tenth Doctor created K9 Mark IV to replace K9 Mark III , he added a shiny metallic blue paint job and other improvements , including an omniflexible hyperlink facility . ( TV : " School Reunion " ) Later , though , K9 reverted to his old dark green colour . ( TV : " Invasion of the Bane " ) In battling Mr Smith ( and following the battle ) K9 displayed a teleport facility and a laser weapon similar to the previous K9s ' . ( TV : " The Lost Boy " ) After K9 Mark I regenerated into K9 Mark 2 , his design was radically altered . His ear probes were replaced with larger silver aerials . A set of blue lights on his head flashed when he spoke . Most of his body was dark silver and a silver dog bone was located under his neck . He seemed to have the same capabilities as Mark I but was presumably more advanced . ( TV : " Regeneration " ) After K9 Mark 2 ' s apparent rejuvenation , he looked similar to his predecessor , but with a bright blue coat of paint and K9 Mark I ' s old collar . ( TV : " The Eclipse of the Korven " ) Known K9 units . K9 Mark I was created about the year 5000 by Professor Frederick Marius , who gave the dog to the Fourth Doctor and Leela . He was left behind with Leela on Gallifrey . ( TV : " The Invasion of Time " ) Some time later , he was blown up by a bomb on Gallifrey , ( AUDIO : " Imperiatrix " ) but survived . This model came to an end when Alistair Gryffen ' s Space - Time Manipulator randomly pulled him to London in the year 2050 . There , he almost immediately self - destructed to protect Gryffen and a group of teenagers from Jixen warriors . ( TV : " Regeneration " ) K9 Mark II was created by the Fourth Doctor as a " backup " when it became obvious that the Mark I was becoming erratic . ( AUDIO : " The Time Vampire " ) He was left behind with Romana II in E - Space , ( TV : " Warriors ' Gate " ) and apparently made it back to Gallifrey when she became Lady President of the High Council . ( WC : " Shada " , AUDIO : " Gallifrey " ) K9 Mark III was a gift from the Doctor to Sarah Jane Smith ( TV : " A Girl ' s Best Friend " ) . This K9 was broken for many years , until he was repaired by the Tenth Doctor . This K9 also had a " maximum defence mode " , as well as offensive capabilities , such as a nose - mounted laser gun . He sacrificed himself to save Deffry Vale High School from Krillitane s . ( TV : " School Reunion " ) K9 Mark IV was a recreation and enhancement of the Mark III created by the Tenth Doctor as a second present for Sarah Jane . ( TV : " School Reunion " ) This model continued in service to his mistress , Luke Smith , Clyde Langer , and Rani Chandra and was known by Maria Jackson and Kelsey Hooper . He was left fixing a black hole in Sweden for many years , but after returning to Earth , was used sparingly , until he went to university with Luke Smith . ( TV : " The Nightmare Man " ) K9 Mark 2 was the result of the activation of the Mark I ' s onboard regeneration unit . He had only very limited memories of his past as the Mark I . He had many adventures with Alistair Gryffen , Jorjie Turner , Darius Pike and his new master Starkey . ( TV : " Regeneration " , " The Bounty Hunter " ) Orthrus was an attempt by Drake and the Department to replicate K9 , but it was of vastly inferior design . ( TV : " Jaws of Orthrus " ) A K9 unit travelled in Ecto - Space with the Mistress . ( AUDIO : " The Choice " , " The Search " )