<Tr> <Th> Home era </Th> <Td> 51st century 20th - 21st centuries </Td> </Tr> <Tr> <Th> Catchphrase </Th> <Td> Affirmative </Td> </Tr> <P> 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 K9 (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 . </P> <P> Within the series' narrative, K9 is a robot dog acquired by Doctor Who's title character in the 1977 serial The Invisible Enemy . The first two incarnations of the character travelled alongside the fourth Doctor (portrayed by Tom Baker) until 1981 . In these stories, K9 proved useful for the powerful laser weapon concealed in his nose, his encyclopaedic knowledge and his vast computer intelligence . By 1981, each of the two models of K9 which travelled alongside the Doctor had been left with one of the Doctor's female companions . The character subsequently transitioned into spin - off territory . Producers hoped K9's popularity with children would launch the series K9 and Company, led by actress Elisabeth Sladen in the role of companion Sarah Jane Smith alongside a new K9 . In 2006, K9 reappeared in the revived series of Doctor Who . Although the character's appearances in the 2007 spin - off The Sarah Jane Adventures were hampered by the concurrent development of the K9 spin - off, the character began to appear full - time in both K9 and The Sarah Jane Adventures, depicting adventures of the original K9 Mark I and of Mark IV, respectively . </P>

When did k9 first appear in doctor who