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)
Consequences that may occur from this is that the dog ends up not being able to work well with the police in a certain situation, which can have extremely serious effects. In this case, the police must state the problem to the personal dog trainer, so that the K9 trainer can teach the dog and the K9 handler how to fix any mistakes that could have been made by the handler.
K9 Mark III first appeared in "A Girl's Best Friend", the 1981 pilot for a series, K-9 and Company, which never materialized beyond the first episode. In this, the character is presented to the Doctor's former companion Sarah Jane Smith (Elisabeth Sladen); together, the two embark on what a number of adventures. Only the first of these is depicted on-screen; several are shown in comic book and audio play adaptations, and others are alluded to by the television series. Mark III made a brief appearance alongside Sarah Jane in the Doctor Who 20th anniversary ninety-minute special The Five Doctors (1983), before appearing properly and for the final time in the revived series' episode "School Reunion" in 2006. By the time of that story, Mark III has fallen into disrepair and eventually sacrifices himself to stop a plot by the alien Krillitane and defeat their leader, Lucas Finch (Anthony Head). In the episode's conclusion, the Doctor presents Sarah Jane with a new K9 to encourage her to continue investigating alien activity; the Doctor "rebuilt" him after the Mark III's sacrifice, implying that he had the same mind and memories as his predecessor while still being a "brand new model".
K9, occasionally written K-9, is the name of several fictional robotic canines (dogs, the name being a pun on the pronunciation of "canine") in the long-running British science fiction television series Doctor Who, first appearing in 1977. K9 has also been a central character in three of the series television spin-offs: the one-off K-9 and Company (1981), The Sarah Jane Adventures (2007–2011) and K-9 (2009–2010). Although not originally intended to be a recurring character in the series, K9 was kept in the show following his first appearance because he was expected to be popular with younger audiences. There have been at least four separate K9 units in the series, with the first two being companions of the Fourth Doctor. Voice actor John Leeson has provided the character's voice in most of his appearances, except during Season 17 of Doctor Who, in which David Brierley temporarily did so. The character was created by Bob Baker and Dave Martin, to whom rights to the character still belong; consequently, Baker's spin-off series K9, which is not BBC-produced, cannot directly reference events or characters from Doctor Who, though it attempts to be a part of that continuity.