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 to N-Space, K9 joined her on Gallifrey. Once on the Time Lords' 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)

First travels
After having made some "tweaks" to the K9 Mark II model, the Fourth Doctor introduced K9 to his new companion, Ann Kelso. He indicated that she would be K9's "new Mistress". (AUDIO: Planet of the Drashigs) The new K9 retained all data and experiences from the previous model, (AUDIO: The False Guardian) including memories of past travels with the Doctor, though he now had, in the Doctor's words, a "few modest improvements". After a particularly rambunctious landing, K9 offered to discover the fault in the TARDIS which had disrupted their course.

Though the Doctor told K9 to stay in the TARDIS while they stepped outside, Ann quietly gave him a counter-order: to wait as they get away, and then to follow. On reuniting with Ann and the Doctor, K9 was asked by the Doctor to use his laser weapon to scare off some approaching Drashigs. The second laser beam severely drained his new power supply, however, rendering K9's motor functions temporarily impaired. He remained in that spot, on 2% capacity, until Trencher discovered him. She brought him to DrashigWorld centre, where Ann made sure he could recharge. (AUDIO: Planet of the Drashigs)

As the TARDIS crew investigated the activities of the Syndicate, the Doctor and K9 learned that "Ann Kelso" was actually a programmed cover identity for Space Security Service officer Anya Kingdom, working as an agent for Zaal, the head of the SSS and the leader of the Syndicate, manipulating the Doctor and K9 into helping Zaal dispose of his enemies. After the Doctor learned the truth, he instructed K9 not to consider 'Ann' his mistress any longer. Although the Doctor was able to determine that Anya had been programmed even in her own identity, he and K9 declined to travel with Anya after the crisis was over, as the Doctor had genuinely liked Ann and found it hard to see Anya as anything other than the reason Ann wasn't there. After the two departed in the TARDIS, K9 noted that he would miss Ann, which the Doctor agreed with. (AUDIO: The Perfect Prisoners)

K9 was kidnapped from the TARDIS by Firandel and Rolgot using a gravatronic tractor beam which they’d intended for the Doctor. K9 overpowered them and was then retrieved by the Doctor. (COMIC: K-9’s Finest Hour)

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. He also fought the Pirate Captain's robot bird. (TV: The Pirate Planet)

K9 helped apprehend the Cessair of Diplos and helped Romana find the Doctor on the Megara ship. (TV: The Stones of Blood)

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 transmatted 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 Daleks 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 were 5000 Daleks that 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 Daleks and Davros. (TV: Destiny of the Daleks) After his voice returned, K9 sounded different for some time. (TV: The Creature from the Pit, Nightmare of Eden, The Horns of Nimon)

K9 remained patiently in the TARDIS while the Doctor and Romana visited Paris. (TV: City of Death) K9 accompanied them to the Queen’s re-coronation (PROSE: The Dying Days) and a conference on Mars. (PROSE: Beige Planet Mars)

After arriving on a confectionary planet, the Doctor and Romana realised K9 was moody because they’d forgotten his birthday. Romana took the TARDIS to Barastabon to fetch a dedicated sponge cake from the Masterbakers of Barastabon for him, however it came to life. K9 suggested releasing it so it could live out its life on the confectionary planet. (PROSE: Special Occasions 1: The Not-So-Sinister Sponge)

On Chloris, K9 attacked some Wolfweeds 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)

When two ships, the Empress and the Hecate, collided in space and the Mandrels were released, K9 helped fight them off with laser beams. He also assisted in uncovering a drug smuggling conspiracy by Tryst. (TV: Nightmare of Eden)

K9 and the Doctor investigated the planet of Skonnos, where the Nimon were planning to invade. He helped stop them by navigating the Doctor through complex tunnels to escape and informed the Doctor of the history of the Skonnan Empire. Soldeed incapacitated him and send him off to examination. (TV: The Horns of Nimon)

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 Femdroids' central processor. Shortly afterwards, with the help of Romana, he realised that Galatea was based on him. (PROSE: The Well-Mannered War)

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 Vardans 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)

K9 was left inside the TARDIS when the Doctor and Romana went punting 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)

The Doctor, Romana and K-9 went on holiday to Cimmerian II, Romana and K9 spent three days trying to find souvenir but couldn't find one. When the TARDIS was impounded, he had charge up in the public portals. He went with the Doctor into the Witness Protection Universe. He generated a sonic field to capture the Children of Pyxis. (AUDIO: 'The Doomsday Contract'')

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 were 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)

He went with Romana to track the Ecidien Cerebus Bird. After Romana was taken by a Laan, he helped the Doctor to try and track her on Earth. He later helped the Doctor to pilot the TARDIS through the second gateway and avoid a missile. (AUDIO: The Pursuit of History)

The Doctor and K9 followed Cuthbert to 2079 and learnt that the Conglomerate had the food to save a race but weren't using it. K9 wanted to know why Cutbert wanted to destroy an Iron Age settlement. (AUDIO: Casualties of Time)

K9 was damaged when he tried attacking some Wrarth Warriors. 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) One account claimed K9 was not present during these events, instead being away with Romana. (AUDIO: 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 Daleks 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)

In London in 1899, he posed as an act at the New Regency Theatre to trace the energy pulse. After Henry Gordon Jago disappeared from the theatre, he acted as the Master of Ceremonies. He managed to stun Jago to stop him mutating. As the Doctor had left the coordinate programme running, K9 managed to trace the TARDIS to Nicholas Asquin's house. (AUDIO: The Beast of Kravenos)

Landing in a battlefield, he had to defend the Doctor and Romana from a group of hostile humanoids, but they were rescued by several Sontarans. He was able to stun the zombie Sontarans. Romana asked him to scan Varn. He detected chronons in Varn's brain. (AUDIO: The Eternal Battle)

In Hollywood in 1930, he detected strange energy readings and informed Romana of this. When Lorretta Waldorf's voice was taken, he examined her vocal chords to see what was wrong. After the Doctor didn't return from his work, he and Romana went to look for him. K9 acted as a satnav when the cab driver took them on a longer route. (AUDIO: The Silent Scream)

Whilst on a beach in Brighton, K9 went into the water and had his circuits damaged. (TV: The Leisure Hive) The Doctor and Romana were trying to repair him when they were caught in a time loop caused by Meglos. Upon being repaired, K9 tried to find the Doctor and Romana, only to shut down in the forests of Tigella. He was eventually able to help defeat Meglos. (TV: Meglos)

The Doctor ordered K9 to install the coordinates to Gallifrey in his circuits. When the TARDIS became trapped in E-Space, K9 helped defeat a group of Marshmen that had risen from the swamp to attack the Alzarians. (TV: Full Circle)

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 winds, 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 Tharils 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)

He worked as Romana's presidential aide. He could easily communicate with his older model. Using the energy signature which emanated from Gryben and extrapolated the arming sequence of the Timonic Fusion Device. (AUDIO: Weapon of Choice) When Leela and her K9 went to a fake temporal summit, he used the "inferior" K9 as a way to access what was happening outside the debating chamber. Romana was worried that this would be monitored, but he reassured her as both units energy signatures appeared as one. (AUDIO: Square One)

K9 analysed data in the Matrix about Project Alpha during the inquiry into the Timonic Fusion Device affair and accidentally activated a data bomb. He used all of his energy to stop it exploding, requiring shutting down his auditory circuits which meant he couldn’t hear Romana’s orders when she decided to let it detonate. K9 Mark I deactivated him so that the bomb exploded. (AUDIO: The Inquiry)

He piloted Romana's presidential TARDIS to the parallel timeline to get to Leela and Cecelia Pollard. (AUDIO: A Blind Eye)

He tracked his other self to find out where Leela went missing. In the vaults, he was the only one that his other self would react to. He informed Leela and Romana who Pandora was. He trapped Pandora in the Matrix and stunned Narvin. (AUDIO: Lies)

He worked with his older counterparts to create a full partition to contain Pandora in the Matrix. (AUDIO: Pandora) Afterwards Romana used K9 to interface with the Matrix and to interact with Pandora. (AUDIO: Insurgency)

He informed Romana that Pandora was gaining more control over the dark partition. He now used the Coronet of Rassilon to access the Matrix. He was overwritten by Pandora as a way to get her release. She released him to enable was able him to disarm all the bombs threatening the chapters and the High Council, in return for Romana putting on the Coronet so she could manifest. Afterwards he remained under her control, helping her escape the cells when Romana had her arrested. (AUDIO: Imperiatrix)

He served with Pandora in the Gallifreyan Civil War. Pandora asked him to find Romana and her bolt-hole and kill Leela, Narvin and Matthias in the process. He installed a visualiser in Pandora's office. He came after Leela, revealing he had begun to fight against Pandora's conditioning, to give her and Narvin a matter transmitter Braxiatel had left him so the could rescue Romana from the Anomaly Vaults. He then tried to lead the guards off their scent. (AUDIO: Fractures)

He hid Romana's activity in the Matrix from Pandora and said that he was perfecting a technological variant of the Dogma Virus, though Pandora grew impatient with him. He helped Romana to defeat Pandora in the Matrix. (AUDIO: Warfare)

After the war he spent his time searching the Capitol to make sure that its systems weren't infected by the technological variant of the Dogma Virus. He informed Romana that the Transduction barriers had failed and that the Sunari had invaded. He went missing during the invasion. Leela found him and took him to Narvin. Narvin used his circuitry to restore communications and the transduction barriers. (AUDIO: Appropriation)

Under Narvin's suggestion he became Romana's legal counsel. He then helped Leela to search K9's office. (AUDIO: Mindbomb)

He predicted that Romana would go to the House of Heartshaven after her exile from the Capitol. Whilst there he accidentally caused Janartis to regenerate and activated the Dogma Virus. He secretly worked with Braxiatel to get the Biodata Archive off the planet, being timescopped along with it. (AUDIO: Panacea)

When they travelled to an alternative Gallifrey he had to calculate where the portal they travelled through had moved. When Leela was inaugurated as president, she made him Castellan. (AUDIO: Reborn)

On a another Gallifrey he identified another version of the Doctor. Returning back to the Axis, he helped Braxiatel to scan the systems when they started to collapse. He thought that it might be due to two versions of the same person being on the Axis. (AUDIO: Disassembled)

He stayed behind on the Axis to take over Braxiatel's role. He told Romana that there was something wrong with the Gallifrey they were exploring. (AUDIO: Annihilation)

On the final Gallifrey he told Romana that the portal was moving. He helped Romana to work out why this version of the eye of harmony wasn't complete and discovered the Krillig. He was trapped on the Axis when he stopped the Krillig from entering the Axis. (AUDIO: Forever)

K9 managed to escape into the prime Gallifrey after the Axis was invaded by the Daleks. (AUDIO: Ascension)

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 Daleks. (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)

K9 once claimed to be devoid of emotional circuitry. (PROSE: Shada)

Behind the scenes

 * In the webcast Shada, K9 mentions that Earth's soil interfered with his traction (an in-joke referring to the original prop's real-life difficulty travelling in a straight line).

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.

'BBV K9'
Bob Baker and Dave Martin gave BBV Productions permission to use this K9 for Adventures in a Pocket Universe. The story implies, but does not confirm, that this version of K9 is in fact K9 Mark II, who had remained in E-Space with Romana II after the events of Warriors' Gate, while the Mistress is implied to be Romana herself. Though BBV Productions was able to secure the original actors for those two roles and the rights to K9 from Baker and Martin, they had no rights to the character of Romana or the concept of E-Space, so in the audios, K9 instead travels with an unnamed woman in Ecto-Space; thus, no direct link could be established or inferred. As such, this wiki considers the two portrayals of K9 to be distinct entities.