Whereas Sarah Jane lifted K9 Mark III into and out of her car, (TV: A Girl's Best Friend) K9 Mark IV had a "hover mode" allowing him to negotiate the stairs of the Smiths' three-story house and bi-level attic, and to enter and exit cars. (TV: The Wedding of Sarah Jane Smith, The Gift) The Eleventh Doctor implied that Mark IV was not the first to have the ability to hover. (TV: The Power of Three)
K9 Mark IV was a recreation and enhancement of the Mark III created by the Tenth Doctor as a second present for Sarah Jane. (TV: School Reunion) This model continued in service to his mistress, Luke Smith, Clyde Langer, and Rani Chandra and was known by Maria Jackson and Kelsey Hooper. He was left fixing a black hole in Sweden for many years, but after returning to Earth, was used sparingly, until he went to university with Luke Smith. (TV: The Nightmare Man)
In 1990, an unspecified K9 unit appeared with Sylvester McCoy as the Seventh Doctor and Sophie Aldred as Ace in an episode of the children's education programme Search Out Science entitled Search Out Space, which was included as an extra on the release of the Doctor Who story Survival by the BBC. Another unspecified K9 unit also appeared in the 1993 charity special Dimensions in Time. In the 1998 computer game Fallout 2, the Navarro base has a damaged robot dog known as K9, which uses similar speech mannerisms to the Infobox Doctor Who character. If repaired, the cyberdog is willing to join the character's party as a companion. In the 1999 television series Queer as Folk (written by future Doctor Who executive producer Russell T Davies), a K9 model is given to the character Vince as a birthday present. The prop used was an original, operated — as occasionally in Doctor Who — by visual effects assistant Mat Irvine. In the second series of I'm Alan Partridge (2002), the character of Alan Partridge recalls how his purchase of the rights to K9 contributed to his mental breakdown and driving to Dundee in his bare feet while gorging on Toblerone. In the South Park episode "Go God Go XII" (2006), Eric Cartman, being trapped in the year 2546, has acquired a robot dog called "K-10", a parody of K9. Due to timeline alterations, he is replaced by robot cat "Kit-9" and later robot bird, "Cocka-3". K9 appeared on a special Doctor Who-themed edition of The Weakest Link in 2007, but was voted out unanimously at the end of the first round, despite answering his question correctly. This was due to the fact every single player of the team answered correctly and banked the £5,000 target, and that the producers told the contestants to vote him off, just in case he broke down. Anne Robinson (whom K9 addressed as "Mistress") said "I'm so sorry" before declaring him the weakest link.
On 24 April 2006, The Independent, the Daily Star and The Times confirmed, following previous rumours, that K9 would be featured in a 26-part children's series, K9, to be written by Bob Baker. The article in The Times also featured a picture of the redesigned K9 for the animated series. The series will be a blend of live-action and a CGI K9.
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 knowledge of tennis from his memory banks. (TV: The Stones of Blood) In another he took Romana's exclamation "Blast it!" as a command, and fired his blaster. (TV: Shada, WC: Shada, AUDIO: Shada, PROSE: Shada). Despite this, he occasionally showed a sense of humour, jokingly answering the question "What do you eat?" with "Ball bearings" (AUDIO: The Beast of Kravenos).
K9 Mark I was created about the year 5000 by Professor Frederick Marius, who gave the dog to the Fourth Doctor and Leela. He was left behind with Leela on Gallifrey. (TV: The Invasion of Time) Some time later, he was blown up by a bomb on Gallifrey, (AUDIO: Imperiatrix) but survived. This model came to an end when Alistair Gryffen's Space-Time Manipulator randomly pulled him to London in the year 2050. There, he almost immediately self-destructed to protect Gryffen and a group of teenagers from Jixen warriors. (TV: Regeneration)
A short story, "Moving On", in Virgin Publishing's Decalog 3: Consequences anthology and the Big Finish Productions-produced Sarah Jane Smith audio play Mirror, Signal, Manoeuvre (both written by Peter Anghelides) indicate that K9 Mark III broke down and Sarah was unable to repair it as the replacement circuits would not be invented for several centuries.