K9

for the TV series see K-9 (TV series)

K-9 is the designation given to a series of intelligent dog-like androids who have served as companions for the Doctor, Leela, Romana and Sarah Jane Smith. The robots' name is often presented as K9 with no hyphen (The Adventures of K9).

K-9 Mark I
Professor Marius invented the first K-9 because weight requirements did not allow him to bring his real dog from Earth into space (DW: The Invisible Enemy) though K-9 may owe his existence to a temporal paradox. According to one account, the professor copied the remnants of one of the version of K-9 created by the Doctor and given to Sarah Jane Smith. (DWM: Tautology)

The Professor offered K-9 to the Doctor as the same weight requirements made him unable to take Mark I back to Earth with him. (DW: The Invisible Enemy) After a number of adventures with Leela and the Doctor, Mark I decided to stay on Gallifrey with his "mistress". (DW: The Invasion of Time). There are (possibily apocryphal) accounts that this model of K-9 later performed missions on behalf of the Time Lords and was given control of a space vessel called K-NEL (The Adventures of K9: K9 and the Time Trap, et al).

K-9 Mark II
At some point prior to this, the Doctor obtained or constructed at least one (possibly more) backup models of K-9, and immediately after leaving Mark I behind with Leela, the Doctor unpacked K-9 Mark II.

Mark II travelled with the Doctor and Romana for an indeterminate period of time, although he became increasingly subject to disrepair (DW: The Leisure Hive). At one point, for reasons unknown, his vocal track programming was changed and he spoke with a different voice (DW: The Creature from the Pit through to Shada). Eventually, Romana and K-9 Mark II left the Doctor together, deciding to stay in E-Space (K-9 had suffered damage that made returning to N-Space unfeasible at the time). (DW: Warriors' Gate) Eventually, however, Romana and the presumably repaired K-9 returned to their own universe, and K-9 Mark II came to live on Gallifrey. (NA: Lungbarrow, WC: Shada)

The fates of K-9s Mark I and II in light of the Last Great Time War remain unknown.

K-9 Mark III
"K-9! Rose Tyler, Mickey Smith, allow me to introduce K-9! Well, K-9 Mark III, to be precise."

- The Tenth Doctor introducing K-9 to Mickey and Rose

A third model, K-9 Mark III (again either obtained or constructed by the Doctor) was given in the late 1970s to Sarah Jane Smith. (KAC: A Girl's Best Friend) Mark III served as Sarah Jane's companion for an indeterminate period of time before ceasing to function; Smith, unable to find anyone to fix the robot, continued to carry K-9 in the boot of her car, until a chance encounter with the Doctor in the mid-2000s resulted in K-9 being restored to functionality. This served to be only temporary, however, as Mark III destroyed itself in order to help the Doctor and his companions defeat a Krillitane invasion (DW: School Reunion).

K-9 Mark IIII
"There was a scientific experiment in Switzerland, they created their own black hole. If it gets free the Earth will be swallowed up. So K-9 is sealing it off."

- Sarah Jane Smith

Afterwards, the Doctor presented Sarah Jane with a replacement, dubbed K-9 Mark IV. (DW: School Reunion) (It's not known if the Doctor quickly built Mark IV from scratch or had it in storage). Mark IV continued on as Sarah Jane's companion, assisting her in her private investigations of alien activity in London. At one point, however, K-9 Mark IV was tasked to help contain a black hole and left Earth, though he was able to occasionally communicate with Sarah Jane via a subspace portal linked to 13 Bannerman Road (SJA: Invasion of the Bane; The Lost Boy). In extreme circumstances, Sarah Jane could also recall K-9 to Earth, as she did when she needed K-9's ability to work out the access code to the Doctor's TARDIS. (DW: Journey's End).



Personality
K-9 had a very consistent personality from model to model. He had a polite, formal manner with just a hint of pedantry bordering on condescension. Though he often displayed feelings such as sorrow (DW: The Invasion of Time) and self-regard (DW: School Reunion), he often stated that he had not been programmed to have emotions.

He did not use contractions just as "you've" for "you have" and addressed others by titles such as "Master", "Mistress", "Doctor-Master" (to refer to the Doctor) or "Young Master" (Adric and in one instance Clyde). Though he did not seem to resent his subordinate status, he tended to side with the Doctor's companions over the Doctor himself and at times showed a dark side, regarding other artificial intelligences with contempt (DW: The Invasion of Time) and relishing a brief chance to act as a figure of power (MA: The Well-Mannered War) He usually did not engage in computer-like literal thinking, though on one occasion he followed Romana's instructions to "forget it" to the letter and erased all his knowledge of tennis from his memory banks. (DW: The Stones of Blood)

Marks

 * K-9 Mark I left behind with Leela on Gallifrey.
 * K-9 Mark II left behind with Romana in E-space.
 * K-9 Mark III left behind with Sarah Jane Smith on Earth.
 * K-9 Mark IV a new body for Mk III when it was destroyed in a Krillitane invasion.

Behind the Scenes

 * In an interview, the writers originally wanted to name K-9 "Pluto", after the Disney character; however, Disney refused permission.