Introduced into the plot in The Invasion of Time, K9 Mark II first actually appear on-screen in The Ribos Operation (1978). More mobile than his predecessor, Mark II exhibited the ability to sense and warn others of danger. He travels as a companion alongside the Doctor and Romana. Around the time of Romana's regeneration (the transition from actress Mary Tamm to Lalla Ward), the K9 character was explained as suffering from "laryngitis" to accommodate Leeson's departure from the series at the start of the 1979–80 season; for this time, he was portrayed by David Brierley, until Leeson's return for the 1980–81 season. When the Doctor and Romana travel to the parallel universe of E-Space, K9 is severely damaged, in Warriors' Gate (1981). The damage was such that K9 could only function in E-Space; when Romana decided to stay and forge her own path, the Doctor gave K9 to her. The character makes subsequent appearances in remakes of the unfinished serial Shada, alongside the Eighth Doctor (Paul McGann); the 2003 Shada audio play and webcast depict K9 Mark II as having returned to Gallifrey with Romana, now Lady President of the Time Lords, where the Doctor visits them. It is not clear if either of these audio appearances are considered canonical in relation to the continuity of the TV series.
The original K9 model was designed by visual effects designer Tony Harding. One early concept was to have a small actor in a large Doberman-shaped costume; however, Graham Williams vetoed this, saying that the robot should not look like a person in a costume. The eventual design was closely based on Harding's third concept sketch. (DCOM: The Invisible Enemy)

In 1996, Sarah used K9 to hack into records and find Sam Jones' home address and later to translate Lost Boy's speech. (PROSE: Interference - Book One) K9 was briefly possessed by a malevolent entity, but was freed when Sarah accidentally electrocuted him. (PROSE: The Sow in Rut) K9 began slowly breaking down and eventually ended up deactivated in a cardboard box in Sarah's attic. (PROSE: Moving On) Hilda Winters had K9 dismantled and analysed. (AUDIO: Mirror, Signal, Manoeuvre)
After K9 Mark I regenerated into K9 Mark 2, his design was radically altered. His ear probes were replaced with larger silver aerials. A set of blue lights on his head flashed when he spoke. Most of his body was dark silver and a silver dog bone was located under his neck. He seemed to have the same capabilities as Mark I but was presumably more advanced. (TV: Regeneration)
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.
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.[citation needed]

K-9 University has spent years refining our services to offer the highest quality resort-like experience for your pet. We work hard to offer individualized attention so that every pet has a safe, comfortable stay while you are away. Our Plano and Garland Dog Day Care and Boarding Services encourage active fun. Dogs are evaluated and based on their similarity they are then sorted into play groups, creating an excellent fit for furry friends!
A K9 officer and his or her dog, should undergo lessons in maintaining the police dog normative once a week. A K9 handler and a police dog improve their work per Shutzhund dog training, tracking training, bomb detection, and K9 tactics. We simulate different situations that may pop up during serious police work, using automobiles, a garage, sport , elementary schools, shopping centers, etc.
The practical challenges of working with the K9 prop have accompanied the robotic pooch in his return to Doctor Who. Producer Russell T Davies told SFX magazine, "Yes, just as we expected, multiple takes [were required] when he bumped into a door or veered off to the left. Lis Sladen did warn us, and she was right!"[7] 2009 saw two different incarnations of K9 appear regularly in two Doctor Who spin-offs: Mark IV in the third series of BBC production The Sarah Jane Adventures, and a re-vamped Mark I in the Park Entertainment production K9.
After this he was tricked by Thorne to give him his regeneration unit for a lost memory chip. This turned him into a bomb to make him self-destruct on encountering Jixey. Starkey helped him disarm himself. (TV: Hound of the Korven) K9 Mark 2's brief life was almost cut tragically short when after the fall of the Korven invasion force, Thorne sent the Trojan to kill K9, who defeated it by burning out his power core and exhausting all his energy. As his regeneration unit was in the Trojan, K9 seemingly died at the mansion after his companions bade him farewell. However his regeneration unit homed in at the last minute and resurrected him, giving the frisky pup a new lease on life. The regeneration unit restored his old dog collar so he could celebrate the joyful occasion to the full as he flew off to more adventures, bristling with life. (TV: The Eclipse of the Korven)

K9, retroactively "K9 Mark I" (Leeson), initially appeared in The Invisible Enemy (1977) as the creation of Professor Marius (Frederick Jaeger) in the year 5000. K9 subsequently travelled with the Fourth Doctor (Tom Baker) and Leela (Louise Jameson) as a companion of the Doctor in his adventures in time and space until The Invasion of Time (1978). In this serial, K9 decides to remain on the Doctor's home planet of Gallifrey with Leela. Immediately afterwards, Doctor Who would introduce a second incarnation of K9, played by the same prop; the last scene of The Invasion of Time shows the Doctor unpacking a box labeled "K9 Mk II".

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