K9 Mark I K9 Mark I or K9 Mark 1 ( TV : " Regeneration " ) was a portable computer originally owned by Professor Frederick Marius , who considered the robot dog his " best friend " . Together , they conducted advanced medical research at the Bi - Al Foundation for an unknown length of time . When the Fourth Doctor and Leela arrived at the Foundation , Leela quickly became enamoured of the dog . The professor eventually gave the dog to the time travellers as thanks for defeating the Swarm . ( TV : " The Invisible Enemy " ) The Mark I was particularly associated with and protective of Leela . Therefore , when she elected to remain on Gallifrey , he also chose to stay behind with her . ( TV : " The Invasion of Time " ) Nevertheless , he occasionally left Leela ' s side when he was sent on solo missions by the Time Lord s . During these adventures he travelled in a spacecraft the Time Lords build especially for him called " K - NEL " . ( PROSE : " K9 and the Missing Planet " , and others ) He eventually came into the service of Lady President Romana II when Romana tapped Leela as her personal bodyguard . Together , Leela and the Mark I went on many missions together at Romana ' s request . He was a vital link between the two ex - companion s of the Doctor , since he could easily and silently interface with Romana ' s K9 unit . ( AUDIO : " Square One " and others ) The unit ' s ultimate fate was considerably unclear , since two radically different accounts existed . According to one , he was utterly destroyed in an explosion and Leela adamantly refused to have another model built in its place . ( AUDIO : " Imperiatrix " ) The other held that he somehow ended up on 21st century Earth , where he was forced to self - destruct when facing the Jixen , engage his regeneration unit and become K9 Mark 2 . Thereafter he accepted a boy named Starkey as his new master , and had several adventures on Earth in the 2050s . ( TV : " Regeneration " ) Later models — or " marks " — of K9 were based on this one . Biography . Creation . Professor Frederick Marius had a dog called Kelso . He couldn ' t take Kelso with him to his new workplace at the Bi - Al Foundation . So he constructed K9 six months before he was leaving Earth , working on it day and night . He used all the latest technology . The heart of the machine was Professor Marius medical computer . A state - of - the - art intraresponsive brain app was added inside it . This allowed K9 to talk . Furthermore a huge general knowledgepool was added into the brain . Professor Marius added these parts together creating K9 . ( PROSE : " One Man and His Dog " ) When he first met Leela , Professor Frederick Marius said only that he " had K9 made up " — " not " that he " created " or " designed " the unit — because weight restrictions did not allow him to bring his real dog from Earth into space . ( TV : " The Invisible Enemy " ) One account claimed that K9 may have owed his existence to a temporal paradox . Far from inventing the dog himself , the professor copied the remnants of one of the versions of K9 created by the Doctor and given to Sarah Jane Smith . ( PROSE : " Tautology " ) Meeting the Doctor and Leela . In the year 5000 AD , K9 aided Marius in scanning the Fourth Doctor for the Swarm inside him . He later fought off the humans infected by the Swarm on Bi - Al and on Titan Base , saving the Doctor and Leela ' s lives on several occasions . The Professor offered K9 to the Fourth Doctor to travel in the TARDIS as the same weight restrictions made him unable to take Mark I back to Earth with him . ( TV : " The Invisible Enemy " ) On the TARDIS . Sometime during his travels , he met Robin Hood . ( TV : " The Last Oak Tree " ) The Doctor arrived on Agratis to see the Jewel of Fawton and eat a banquet . However , the Jewel had gone missing , and the Judoon had been called in to reclaim it . While the Doctor searched for the Jewel ' s thief , Leela and K9 distracted the Judoon out of the city so the Doctor could leave ; K9 connected himself to a tank , and Leela hijacked a motorbike . When the species that originally owned the Jewel were discovered , the Judoon ' s search was called off . Becoming much less aggressive , Leela invited them to dine at the banquet . While Leela was feasting with the Judoon , a mysterious cloaked figure kidnapped Leela and K9 . ( COMIC : " A Rare Gem " ) On E9874 , he stunned one of the Tarl s which entered the ship and thought it resembled a Neanderthal . He worked out that there was atypical development when they travelled in a cart . Ergu was interested in him . He recognised a complex symbolic pattern . he was damaged when Gethal kidnapped Leela . He analysed the symbols and found a way to destroy the beacon . ( AUDIO : " The Exxilons " ) K9 stopped an assassin from killing the Doctor , which led the Doctor to devise a plan to find out who wanted him . As part of the Doctor ' s plans , he was reprogrammed obey the Rocket Men leader Shandar . He was fitted with a rocket to help with their raids . He told Shandar that he was in fact the fifth most wanted person in the galaxy , after , the Rani and the Terrible Zodin . After the Doctor was discovered , he stunned the Master and Shandar . The Doctor then asked him to direct him through the asteroid field to destroy the rest of the force field generators . He couldn ' t do the calculations quickly because he was decrypting the codes of the prisoner and slave locks . He generated the facsimile of the Doctor . When the Master tried to escape , K9 stalled the Master ' s TARDIS so he could use it to signal Galactic Heritage . He was an excellent TARDIS pilot . ( AUDIO : " Requiem for the Rocket Men " ) K9 piloted the TARDIS to the coordinates where Marshall had said he had traced the Master and Leela . The Doctor asked K9 to trace Leela through the Death Match ' s arena . He met with the Red Knight who found him funny , and his rocket blew up . This damaged him considerably , and shortly afterwards he had to escape from a set of locusts . He rescued Marshall from the Red Knight . He showed Marshall the loading bay and realised that the machinery there was used to heal Leela . He then helped the Doctor to reverse the transmat and got them out of arena and back to the TARDIS . ( AUDIO : " Death Match " ) He effected a materialisation on Krelos and changed the TARDIS control room . He became infected after this happened by the strange particulates in the room . He started to calculate something and ignored the Doctor ' s commands . He tried to fight the infections . K9 exited the TARDIS and tried to climb after the Doctor and Leela . Re - entering the TARDIS , he told the Doctor that the TARDIS was malfunctioning . He helped the Doctor zone in on Geralk ' s signal . He reported to his new masters that the Doctor and Leela had escaped . Leela noticed that K9 was acting strangely . Now fully controlled , he set the TARDIS on a course for Telos . ( AUDIO : " The Fate of Krelos " ) The Doctor had changed the course he had programmed so that they travelled back in time . This weakened the Cybermen ' s control over K9 . When the TARDIS fell off a cliff , K9 was damaged and the Doctor noticed that there was a Cybermat in his brain . He repaired himself and left the TARDIS . He entered the hibernation chamber with the Robot Drone which the Doctor controlled to stop the cyber nanites from infecting the TARDIS . This rewrote time and K9 wasn ' t infected . ( AUDIO : " Return to Telos " ) He started to act strangely when he and Leela landed on Westtropi III . This including shooting Leela ' s knife out of her hand and telling her not to explore . He was being controlled by a Time Vampire . ( AUDIO : " The Time Vampire " ) K9 participated in the Doctor ' s plan to put the Vardan s in a time loop . In order to effect this , the Doctor had himself inducted as Lord President on Gallifrey . He had K9 destroy the transduction barrier , allowing the Vardans to travel along wavelengths and partially materialise on the planet . When the Vardans , and the Sontaran s who followed them , were defeated , Leela chose to stay behind , having fallen in love with Andred . K9 chose to stay with his " mistress " to look after her . She asked him if the Doctor would be lonely without them , but he could only reply that there was " insufficient data " , which saddened both . ( TV : " The Invasion of Time " ) On Gallifrey . When the Dominator s attempted to conquer Gallifrey , K9 fought alongside Leela against the invading Quark s which had " flooded " the Captiol , destroying 39 between them . ( AUDIO : " Time in Office " ) Following an incident in the Death Zone , K9 accompanied Andred on a clean up in order to dispose of what creatures remained there . ( AUDIO : " Time in Office " ) Though K9 remained on Gallifrey to " protect " Leela , he was occasionally used by the Time Lord s for various solo missions . Towards this end , they gave him a specially built space vessel called " K - NEL " that only he could control , which gave him freedom of movement in space , but not time . ( PROSE : " K9 and the Time Trap " , et al ) K9 was briefly reunited with the Doctor , now in his seventh incarnation , who stopped by to see how Leela ' s development had progressed . The Doctor took the identity tag from K9 ' s collar as a memento . ( PROSE : " Affirmative " ) After the temporary destruction of Gallifrey in the War , K9 became trapped in the Doctor ' s TARDIS . He was ultimately freed by the Eighth Doctor and sent on a mission to the planet Espero . ( PROSE : " The Gallifrey Chronicles " ) K9 was with Leela on Gallifrey for many years , but it was only after the disappearance of her Time Lord husband , Andred , that she and her K9 met Romana II and her K9 . Despite the fact that the two K9 units did not get on well and competed with each other , ( AUDIO : " Weapon of Choice " , " The Inquiry " ) they frequently networked together and allowed easy communication between their respective mistresses . ( AUDIO : " Square One " ) After Leela became Romana ' s bodyguard , and after many important missions on her behalf , Leela ' s K9 was destroyed in a bomb explosion , leaving Leela heartbroken , but refusing to allow a duplicate unit to be built in its place . ( AUDIO : " Imperiatrix " ) After being destroyed . K9 Mark I survived the explosion that Leela and Time Lord technology confirmed had utterly destroyed him . At some point after this event , and indeed after the Last Great Time War , he became an agent of the Korven . ( TV : " Hound of the Korven " ) During this period , he had a number of adventures whose details were not well recorded . For example , the Mark I was known to have gone to the second planet of the Montoon system and observed the Sea of Brains . He also liberated the Anubian s from the Huduct . Furthermore he saved the Glomb Tenklept from being eaten by a Yakoclaw . ( TV : " Curse of Anubis " ) Regeneration . Later , he went to the year 50 , 000 and met Zanthus Pia , head of the Galactic Peace Commission , whom he later saw murdered at the hands of Ahab , a Jixen emissary and his three guards . As K9 was a witness , the Jixen attacked K9 . ( TV : " The Bounty Hunter " ) The Jixen were pulled to 2050 London via a Space - Time Manipulator and tried to warn the humans about a Korven invasion . However , they couldn ' t speak English and the humans believed they were attacking them . K9 came through the STM and attacked the Jixen . After a brief battle he realised his power was running low , and as a last resort to protect the humans , K9 self - destructed , destroying himself and two of the Jixen . Although working for the Korven , he cared for the safety of humans and advised them to evacuate . Using his regeneration unit , the remains transformed into a new incarnation . ( TV : " Regeneration " , " Hound of the Korven " ) Personality . K9 was often left behind in the TARDIS and so he saw journeying out as a treat . ( TV : " The Sun Makers " ) Despite his claims that he was not programmed to feel emotion , he did show a capacity for feeling . He sulked when Leela insulted him , and would only talk to her again after she apologised . The Doctor described him as overbearing , arrogant and insufferable , after K9 told him there was only a 1 % chance of the Doctor having a better explanation for something than him . Andred claimed " If [ he ] had a dog like [ K9 ] in [ his ] unit , [ he ' d ] make him a sergeant " . ( TV : " The Invasion of Time " ) The Doctor once described K9 as one of his best friends . ( AUDIO : " The Exxilons " ) Features . The mechanics of K9 Mark I included rotating ear - probes , telescopic " eye " probe , extendable nose , flashing lights on the top and the " eye " panel , waggling tail antennae , and ticker - tape tongue . The head could also move up and down . The shell was painted in gold / grey metallic . 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 , from which hung a silver disk . ( TV : " The Invisible Enemy " ) By the time of his liberation of the Anubian s , K9 was modified ( likely by the Time Lords or the Korven ) so he could fly through the vacuum of space . ( TV : " Curse of Anubis " ) K9 was capable of calculating 72 variables at once . ( AUDIO : " Requiem for the Rocket Men " ) The Rocket Men installed a propulsion unit in K9 while he was in their possession . ( AUDIO : " Death Match " ) K9 had a vast database inherited by his next incarnation containing data on the following aliens : K9 claimed that he was shaped like a dog because " the human ego requires a familiar reference point to aid in adjusting to new concepts . Animal forms are comforting to the majority of humans . " ( PROSE : " Housewarming " )