The Doctor (Doctor Who)
The Doctor is the title character in the long-running BBC science fiction television programme "Doctor Who". Since the show's inception in 1963, the character has been portrayed by thirteen lead actors. In the programme, "the Doctor" is the alias assumed by a centuries-old alien—a Time Lord from the planet Gallifrey—who travels through space and time in the TARDIS, frequently with companions. The transition to each succeeding actor is explained within the show's narrative through the plot device of "regeneration", a biological function of the Time Lord race that allows a change of cellular structure and appearance with recovery following a potentially fatal injury.
K9 (Doctor Who)
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.