K9 Mark II K9 Mark II was the second K9 known to the Fourth Doctor . He was stored in a box inside the Doctor ' s TARDIS by the time K9 Mark I stayed behind on Gallifrey . ( TV : " The Invasion of Time " ) The unit was particularly associated with Romana , having served both Romana I and Romana II . Indeed , he stopped travelling with the Doctor at the same time as the second Romana , with whom he remained in E - Space in order to assist with the liberation of the Tharil species . When Romana returned into N - Space , K9 joined her on Gallifrey . Once on the Time Lord s ' homeworld , he continued to serve Romana as she ascended to the post of Lady President of the High Council . ( AUDIO : " Weapon of Choice " , " et al " ) Whilst on Gallifrey , he frequently liaised with K9 Mark I , Leela ' s version of the robot , whom he found to be " inferior " . ( AUDIO : " Square One " , PROSE : " Jealous , Possessive " ) Biography . After K9 Mark I decided to stay on Gallifrey with Leela , the Fourth Doctor already had Mark II ( or at least its components ) prepared and in storage in his TARDIS . ( TV : " The Invasion of Time " , AUDIO : " The Time Vampire " ) Quest for the Key to Time . This version of K9 accompanied the Doctor and Romana I on their quest to locate the segments of the Key to Time . The Doctor used a dog whistle to alert K9 and to summon him . ( TV : " The Ribos Operation " ) K9 killed pirates who were attacking other planets from their own , Zanak . ( TV : " The Pirate Planet " ) On Tara , K9 disabled several guards in the employ of Count Grendel of Gracht . He travelled in a boat with the Doctor in a passage under the Count ' s castle , cutting a way through with his blaster . The Doctor left K9 in the boat as he went to foil the Count ' s plot . ( TV : " The Androids of Tara " ) When the TARDIS landed on Delta III , the swampy terrain made it impossible for K9 to accompany the Doctor and Romana . He remained in the TARDIS . ( TV : " The Power of Kroll " ) While searching for the sixth segment , they landed on the planet Atrios . K9 was tricked into entering a scrap metal furnace , but the Doctor rescued him before he was melted . K9 transmat ted to the planet Zeos . K9 told the super - computer Mentalis it was good to talk with someone who was not as illogical or unpredictable as a flesh - and - blood being . K9 again transmatted , arriving on the third planet . He was turned by the Shadow to do his bidding , but the Doctor was able to remove the control matrix implanted by the Shadow , restoring him to his former self . ( TV : " The Armageddon Factor " ) Further adventures . In an attempt to evade the Black Guardian , the Doctor activated the TARDIS ' randomiser and programmed it to visit approximately 1 , 000 planets , which took about a month . He left K9 aboard the TARDIS during this time while he and Romana took up residence in a London townhouse in 1929 . ( AUDIO : " The Auntie Matter " ) In the bowels of the TARDIS , he helped Romana do some repairs . He noticed that something was causing the energy in the TARDIS to be three times the maximum . During the Time Phasing , he started to act strangely . After Romana was involved in a helicopter crash , K9 located her under the sand . He was crushed by a Laan . ( AUDIO : " The Sands of Life " ) After being fully repaired , K9 interpreted the signals from a set of squid in the Mariana Trench . He then helped to find the source of radio interference in the trench which made them loose radio contact with the Doctor and Patricia Sawyer . He became possessed and deliberately drowned Romana and Terri McCulloch . Shortly afterwards , he reasserted himself and helped the Doctor to escape a Jellyfish . He then helped the Doctor to get to a mysterious spaceship . When the Doctor planned to destroy the spaceship , K9 was used as a bargaining chip to stop him from threatening to kill Romana again . After the ship exploded , he contacted the intelligent squid to save the Doctor and then got the engines of the submarine to work again . ( AUDIO : " Phantoms of the Deep " ) When the Doctor landed in the Proxima System , K9 measured the quantities of deadly Zukadom ' s Haze . After detecting the hypersonic frequencies of the Dalek s he came to the rescue and destroyed a Dalek who was going to exterminate the Doctor . He was captured as a Dalek Prisoner and tortured to give the Doctor ' s whereabouts . When he met Mr Dorrick , he was patronised . ( AUDIO : " The Dalek Contract " ) He kept measuring the particles in the Haze and informed Mr Dorrick that they were increasing . When Mr Dorrick asked him to move quietly , he activated a stealth mode which Romana didn ' t know existed . He went to assist the Halka to stop the Dalek security squad on the conglomerate platform . He calculated that there was 5000 Daleks were going to dock with the station . Whilst the Doctor concluded his plan he fought with the Daleks . ( AUDIO : " The Final Phase " ) The Doctor , Romana , and K9 encountered a frog - like being named Bolog , who had a fleet of ships at his command hidden on the far side of the moon . The Doctor was able to stop him by sending his ships into orbit around the sun with a banana . ( COMIC : " Death to the Doctor ! " ) While making repairs to K9 ' s brain circuit , the Doctor found that K9 had contracted laryngitis and could not speak . K9 was left in the TARDIS while the Doctor and Romana II battled the Dalek s and Davros . ( TV : " Destiny of the Daleks " ) Later he remained patiently in the TARDIS while the Doctor and Romana visited Paris . ( TV : " City of Death " ) After his voice returned , K9 sounded different for some time . On Chloris , K9 attacked some Wolfweed s and the soldiers of Lady Adrasta . The Wolfweeds swarmed about him and entwined him in fibres . He was taken by Adrasta , as metal was valuable . ( TV : " The Creature from the Pit " ) K9 was damaged when he tried attacking some Wrarth Warrior s . He was left on board the TARDIS for repairs , during which time he believed he was Leela , and later , a cat . When the Wrarth Warriors arrested Beep the Meep , K9 hissed at Beep . ( COMIC : " Doctor Who and the Star Beast " ) The Doctor repaired K9 . When the Doctor attempted to return Blackcastle resident Sharon Davies home , they instead ended up in the space freighter the " Spacehog " in the New Earth System . K9 stunned a group of attacking Werelox with his nose beam on board the ship , who were then tranquillised . The Doctor was infected by the venom of a Werelok claw and began transforming into a Werelok . He brought K9 into the TARDIS , and hauled the ship out of time and space . He spent three months in the TARDIS laboratory devising a cure , while K9 was under orders to stun the Doctor every time he tried to return to the controls . When the Doctor and K9 returned , only ten minutes had passed on board the " Spacehog " . The Dalek s had used the Werelox as an army to attack the planets of the New Earth System so they could sterilise life there and breed a super race of Daleks in the system out of the qualities of the zoo creatures they kept on board the Dalek battlecraft . When the Doctor was captured on board the battlecraft , K9 released the captured zoo aliens , causing them to attack their Dalek captors . After discovering the Room of the Many Centuries , the Doctor escaped to the TARDIS to materialise the ship inside the room . When K9 and the hypnotised Werelok Brill cleared the secured room of Daleks , the Doctor disconnected the time - space rationaliser of the time transporter , freezing the Daleks in one moment in space and time forever . Sharon decided to continue travelling with the Doctor before returning to Blackcastle . ( COMIC : " Doctor Who and the Dogs of Doom " ) K9 was separated from the Doctor and Sharon by a split in the fabric of space and time that split the TARDIS in two . He reunited with the Doctor and Sharon , both of whom were aged four years by a malfunctioning chrono - compensator , when the two halves of the TARDIS were brought back together . ( COMIC : " Doctor Who and the Time Witch " ) After landing on Barclow , he was given constitutional privilege after trying to warn Rabley about the incoming bomb . Subsequently , he became a presidential candidate . He went to Metralubit to run his campaign . He developed an economic policy that would be populist but not raise taxes . During his campaign , the population of Metralubit started rioting . He was affected when Menlove Stokes destroyed the Femdroid s ' central processor . Shortly afterwards , with the help of Romana , he realised that Galatea was based on him . ( PROSE : " The Well - Mannered War " ) K9 was left inside the TARDIS when the Doctor and Romana went punt ing in Cambridge to meet Professor Chronotis . After several hours of being " nowhere " , ( WC : " Shada " ) due to the Doctor and Romana being taken out of time by Borusa , ( TV : " The Five Doctors " ) the Doctor went back to the TARDIS , demanding everyone to put their bathing suits on as they were going to Brighton . The Doctor and Romana , though retaining memories of the punting trip , had forgotten they intended to visit Chronotis . The Doctor said that they had intended to be back " before lights out " , but " went on somewhere else " , according to Romana , after only being away from the TARDIS for two hours and twenty - one minutes . ( WC : " Shada " ) He went on another wild goose chase to stop the Black Guardian from tracking the TARDIS . After finishing , he arrived in London in June 1964 where he was effected by a wave cancellation frequency modulator . After repairing himself , he went with Romana to Mark Lanchaster ' s pirate radio station and determined that the Vardan s were invading . Returning to the lab , he helped Romana to recreate the modulator in time to stop the invasion . He had recorded the wave modulation cancellation frequency that damaged him and used it to cancel out the Vardans . ( AUDIO : " Wave of Destruction " ) He tried to get the Doctor to stop playing the violin . He tracked the course of the Time Tank which collided with the TARDIS to find Romana . He went after Romana to get her back to the TARDIS . Romana asked him to deactivate the bomb which Embery had planned to use to attack the future . K9 was placed in the bomb and waited until its planned detonation time to rejoin the Doctor . He was taken by Lostar and Tyrus to see Machina . ( AUDIO : " The Paradox Planet " ) Embery wanted to take K9 apart when he went to Era 14 . He remained on the planet after the Doctor was captured , and set up the cult focused around the Doctor and Romana . He told Romana of what happened in the past and that he had been guarding the TARDIS for 1000 years . He was given a message in Era 14 by Romana to tell the Doctor about the bombs in the future . The Doctor set K9 a task to become Machina so that he could deliver all the messages . ( AUDIO : " Legacy of Death " ) He went searching for the parrot in the TARDIS . After Drax dragged the TARDIS off course , he was locked by Drax . Helping Romana to escape , he noticed that there was two fields in operation : one was a temporal grace and the second was a body scrambling . He stunned the twelfth incarnation of Drax to allow Romana to stop a fake auction . ( AUDIO : " The Trouble with Drax " ) In E - Space , K9 led the attack on the castle of the Three Who Rule . He shot many of the guards , doing most of the work . The Doctor made Ivo apologise to K9 for doubting him . ( TV : " State of Decay " ) Damaged by the time wind s , K9 Mark II could not cross back into N - Space with the Doctor , and decided to stay at the Gateway with Romana , to help her free the remaining Tharil s from slavery . ( TV : " Warriors ' Gate " ) Adric greatly missed K9 after he left the TARDIS . ( AUDIO : " Psychodrome " ) The Doctor chose not to replace K9 again , though he did build / obtain a Mark III that he gifted to Sarah Jane Smith ( TV : " A Girl ' s Best Friend " ) and , upon the destruction of Mark III , rebuilt him into K9 Mark IV to give to Sarah Jane . ( TV : " School Reunion " ) On Gallifrey . Mark II was repaired . He accompanied Romana when she returned to N - Space . During Romana ' s term as President of Gallifrey , K9 Mark II served as her aide and advisor . ( PROSE : " Lungbarrow " ) Remembering he had intended to visit his friend , Professor Chronotis in 1979 Cambridge back in the days his fourth incarnation travelled with Romana II , ( WC : " Shada " ) before he and Romana were taken out of time by Borusa for several hours , ( TV : " The Five Doctors " ) the Eighth Doctor came to Madame President Romana and K9 on Gallifrey to investigate what he was supposed to have been doing before his fourth incarnation , annoyed he was " nowhere " for several hours , forgot and went off to Brighton . K9 was able to trace the sphere that attacked the Doctor to the ship of Skagra . The Doctor , Chris Parsons , Romana and K9 travelled to it . Chris and K9 were imprisoned in the ship ' s brig until the Doctor could release them . When the Doctor ' s meddling on board Skagra ' s ship awoke a Krarg , K9 bought time for the Doctor and Chris by fighting it off . The Krarg attacked Think Tank and destroyed its systems . Using " The Worshipful and Ancient Law of Gallifrey " as a " key " , Skagra took Romana with him to the Time Lord prison planet , Shada , to take the mind of the criminal , Salyavin , to make all inhabitants of the universe share Skagra ' s mind . Discovering Chronotis ' TARDIS on board Skagra ' s command ship , the Doctor chased after him . After arriving , Skagra stole the mind of the Professor , who was actually Salyavin . Skagra began placing fragments of the minds he had stolen into his Krarg servants . As Skagra left Shada in the Doctor ' s TARDIS , the Doctor created a tunnel to link the two TARDISes in the time vortex together . This broke Chronotis ' TARDIS . However , K9 was able to help repair it . The Doctor arrived through the TARDIS ' " back entrance " and improvised a mind control helmet to command the Krargs , as part of the shared mind contained the Doctor ' s own thoughts . After the TARDIS landed on Skagra ' s command ship , the conflicting commands from the Doctor and Skagra destroyed the Krargs , the surviving victims whose minds were taken by the sphere returning to their bodies . The Doctor and Romana ordered K9 to shoot at the Krarg commander , leading it towards the vats of unborn Krargs , destroying it and the vats . ( WC : " Shada " ) Personality . K9 was faithful to the Doctor and called him " Master " — calling him " Doctor " only once , and this was when under the control of the Shadow . ( TV : " The Armageddon Factor " ) He corrected the Doctor when necessary . ( TV : " The Ribos Operation " ) He was happy at the prospect of going on holiday ( TV : " The Ribos Operation " ) and to have a conversation with the super - computer Mentalis , declaring it better than talking to unpredictable life forms . K9 branded optimism illogical , bordering on insanity . ( TV : " The Armageddon Factor " ) He declared that he didn ' t feel anything nor did he find it necessary to do so . ( TV : " Warriors ' Gate " ) K9 had no problem with killing those who threatened him , such as Count Grendel ' s men or the guards of the Three Who Rule . ( TV : " The Androids of Tara " , " State of Decay " ) He only killed in self - defence , as his programming dictated . ( TV : " The Creature from the Pit " ) The Doctor and K9 were fond of each other , as the Doctor described K9 as his " best friend " and when they were due to be destroyed in the TARDIS — which they actually survived — the Doctor placed a first place ribbon onto K9 , and K9 thanked him . The Doctor said that K9 had saved his life lots of times . ( TV : " Nightmare of Eden " ) Features . After K9 Mark I was left behind with Leela on Gallifrey , the Doctor built an improved K9 Mark II . Gone was the product of Marius ' 5000 AD technology . This new K9 was a product of the Doctor ' s own technology and values . The gun was now only capable of stunning — not killing — and K9 now responded to a dog - whistle . K9 also featured a vast memory - bank , seemingly a mixture of the Mark I model , the Doctor ' s own memory and knowledge , and that of the TARDIS . ( TV : " The Invasion of Time " ) Unlike Mark I , Mark II could climb stairs , ( PROSE : " Heart of TARDIS " ) but it took a great deal of time and energy . ( PROSE : " The Shadow of Weng - Chiang " ) K9 was also equipped with a stealth mode . However , he did not use it until boarding the space platform " Fortune II " in the Proxima System , as " no one ever asked . " ( AUDIO : " The Final Phase " ) His blaster ray had an accuracy of 98 % . ( AUDIO : " Ascension " ) It was notably deadly against Dalek s . ( COMIC : " Doctor Who and the Dogs of Doom " ) 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 " ) Behind the scenes . Casting . John Leeson provided K9 Mark II ' s voice in almost all appearances . Another actor , David Brierley voiced him in " The Creature from the Pit " , " Nightmare of Eden " and " The Horns of Nimon " , while Roy Skelton , better known as a Dalek voice actor , provided the character ' s voice in " Destiny of the Daleks " when all was required was a croaking sound . Leeson took over the role again from " The Leisure Hive " onward .