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.
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Before this, the Doctor obtained or constructed at least one backup model of K9. Immediately after leaving Mark I behind with Leela, he unpacked K9 Mark II. This version of K9 accompanied the Doctor and his new companion on their quest to locate the segments of the Key to Time, (TV: The Ribos Operation) but the swampy terrain of Delta III made it impossible for him to join them on the planet. At the conclusion of the quest, the Shadow turned K9 to his evil will, giving K9 a sinister personality. (TV: The Armageddon Factor)
The Fourth Doctor and K9 Mark II spent an indeterminate period of time together. However, the Doctor appeared to be activating K9 Mark II, implying that no significant time had elapsed since leaving Gallifrey. (TV: The Ribos Operation) It is possible that the Doctor spent some time at Nest Cottage before activating him. (AUDIO: The Stuff of Nightmares)
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)
Later he defeated Ahab, who tried to convince him he had murdered Zanthus Pia. He became part of the K9 Unit, being made the responsibility of Gryffen and under the control of Department inspector June Turner. (TV: The Bounty Hunter) He foiled Inspector Drake's plan to control the population using Cerulium (TV: Sirens of Ceres) and experienced fear. (TV: Fear Itself) He aided in the defeat of echoes of Gryffen's family, (TV: The Fall of the House of Gryffen) Orthrus, a duplicate of him created by Drake to frame him (TV: Jaws of Orthrus) and the Bodach. (TV: Dream-Eaters) He met Nehetka and Geb of the Anubians, a race his previous incarnation liberated. He was so obsessed with regaining his lost memories that he didn't notice Gryffen, Starkey and Jorjie's takeover by the Anubians. He soon found out when the Anubians attacked the Department. With Darius' help, he defeated them. (TV: Curse of Anubis)
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)
Later he defeated Ahab, who tried to convince him he had murdered Zanthus Pia. He became part of the K9 Unit, being made the responsibility of Gryffen and under the control of Department inspector June Turner. (TV: The Bounty Hunter) He foiled Inspector Drake's plan to control the population using Cerulium (TV: Sirens of Ceres) and experienced fear. (TV: Fear Itself) He aided in the defeat of echoes of Gryffen's family, (TV: The Fall of the House of Gryffen) Orthrus, a duplicate of him created by Drake to frame him (TV: Jaws of Orthrus) and the Bodach. (TV: Dream-Eaters) He met Nehetka and Geb of the Anubians, a race his previous incarnation liberated. He was so obsessed with regaining his lost memories that he didn't notice Gryffen, Starkey and Jorjie's takeover by the Anubians. He soon found out when the Anubians attacked the Department. With Darius' help, he defeated them. (TV: Curse of Anubis)
K9 Mark III was a gift from the Doctor to Sarah Jane Smith (TV: A Girl's Best Friend). This K9 was broken for many years, until he was repaired by the Tenth Doctor. This K9 also had a "maximum defence mode", as well as offensive capabilities, such as a nose-mounted laser gun. He sacrificed himself to save Deffry Vale High School from Krillitanes. (TV: School Reunion)
A third model, K9 Mark III was evidently constructed by the Fourth Doctor; indeed, the Eighth Doctor did not dispute the presumption that he had built this K9. (PROSE: Interference - Book Tqo) Mark III travelled with the Fourth Doctor and Adric for a time. (PROSE: Inter-Galactic Cat) Eventually, however, he was shipped in 1978 to Sarah Jane Smith at the home she had shared with her Aunt Lavinia in South Croydon during her companionship of the Third and Fourth Doctors. (TV: A Girl's Best Friend) Since parting ways with the Doctor (TV: The Hand of Fear) however, Sarah Jane had already gone away and was travelling extensively. The following year, Lavinia purchased a manor house and market garden in Moreton Harwood, Gloucester, and took the still crated K9 with her. On 18 December 1981, Sarah Jane and her foster brother Brendan Richards arrived at Lavinia's home for Christmas, but Lavinia had left early for her lecture series in the United States. Sarah Jane opened the crate and received her new companion. (TV: A Girl's Best Friend)
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)

During an encounter with the sentient painting, the Mona Lisa at the International Gallery, a simulation of K9 Mk IV was created when Mona Lisa was tricked into animating a drawing of K9 made by Clyde inside a cloud of mystic drawing-animation energy. He subsequently defeated The Abomination, another evil painting-come-to-life, before disappearing as the Mona Lisa herself reverted to being an immobile painting. (TV: Mona Lisa's Revenge)
The Virgin New Adventures seventh Doctor novel Lungbarrow (written by former Doctor TV series writer Marc Platt) featured K9s Marks I and II meeting for the first time on Gallifrey during the events surrounding the disappearance of the Doctor's entire family house and his living relatives, which also featured many previous established Gallifreyan based characters. The two collaborated towards rescuing the Doctor, then current companion Chris Cwej and the Doctor's lost family. This novel also served as the direct lead-in story to the 1996 Doctor Who telemovie.
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