K9 Mark II is the main tritagonist of Seasons 16-18 of Doctor Who.
In Seasons 16 and 18, he was voiced by John Leeson, who also voiced K9 Mark I and reprised the role for Big Finish and BBV. In Season 17, he was voiced by the late David Brierley.
Biography
K9 was constructed by the Doctor aboard the TARDIS as a replacement for his predecessor, who had elected to stay behind on Gallifrey. Not long after, the pair were recruited by the White Guardian, along with Romana, to search for the six missing segments of the Key to Time. K9 would often be left behind in the TARDIS during their quest but would usually be called upon at some point to assist his master and mistress, rescuing them from the Graff Vynda-K on Ribos, battling against both the Captain of Zanak's robot parrot Polyphase Avatron and Cessair of Diplos' rock-like servants the Ogri, and aiding the Doctor in avoiding a trap set by Count Grendel and infiltrating Grendel's castle. During their last stop on the twin planets Atrios and Zeos, K9 showed an affinity with the doomsday computer Mentalis and fell under the mental influence of the Shadow, a servant of the Black Guardian. Once restored to normal however, he proved invaluable in helping the Doctor and his Time Lord friend Drax infiltrate the Shadow's sanctum and retrieve the Key, by having them ride inside him while miniaturised.
Having sat out the subsequent two adventures after contracting laryngitis, K9 aided the Doctor and the now-regenerated Romantic on Chloris, where he was disabled by the metal-eating Wolf Weeds. He would defend them against the Mandrels during their adventure on the Empress and guide them out of the Nimon's Power Complex. His usefulness against Skagra's engineered Krarg warriors was limited but he was able to assist in repairs to Professor Chronotis' TARDIS and at one point confronted Skagra as a decoy for the Doctor.
K9 was disabled by seawater during a trip to Brighton and suffered a number of power failures during the later adventure on Tigella. After the travellers were lost in E-Space, K9 proved little better on Alzarius, being decapitated by the Marshmen. After being repaired again, he finally assisted the rebels against the Great Vampire, leading them in a battle against the vampires' guards while the Doctor killed the Vampire King. However, when the TARDIS reached the still point between E-Space and N-Space, K9 was badly damaged by time winds. With Romana having elected to stay there to help free the Tharils from slavery, the Doctor left K9 with her so he could be restored by the gateway.
K9 was one of the stars of BBV's series The Mistress and K9, paired with an owner strongly implied to be Romana but never named. The New Adventures novel Lungbarrow established that he had accompanied Romana back to Gallifrey and he would be a regular character on Big Finish's Gallifrey audio plays.
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