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)

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)
He did not use contractions such 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, Starkey and in one instance, Clyde). Though he did not seem to resent his subordinate status, he sided with the Doctor's companions over the Doctor and showed a dark side, regarding other artificial intelligences with contempt. (TV: The Invasion of Time, TV: The Wedding of Sarah Jane Smith, TV: Robot Gladiators) He relished a brief chance to act as a figure of power. (PROSE: The Well-Mannered War)

When Romana eventually returned to her own universe, she brought K9 Mark II with her (presumably having repaired it) and eventually became Lady President of Gallifrey. K9 Mark II is first seen on Gallifrey in the Virgin New Adventures novel Lungbarrow by Marc Platt, alongside K9 Mark I, which had remained with Leela. Both K9 Mark I and Mark II appear, voiced by Leeson, in the Big Finish Productions audio adventure Zagreus and the Gallifrey audio series. Leela's K9 (Mark I) was destroyed at the conclusion of the second Gallifrey series and only Mark II appears in the third series.
The handler and dog must also be able to pass the police test, which involves controlling the dog fully, even after giving the dog the attack command. The dog must stop immediately and fulfill any command it is given by the handler. There are specifications of training involved in using trained K9 police dogs in the airport, marine ports, railroads, in a metro station.

During Romana's Presidency of Gallifrey, Leela became her bodyguard, and the two K9 units were forced to work together, not always amicably. After Matthias had replaced Romana as President, he nominated her to undertake a mission to find a cure for the Free Time virus, to be followed by exile. K9 opted to remain in the employ of Matthias, fighting the infection on Gallifrey. However, Braxiatel and K9 had planned another operation. Realising that the only cure to the virus was to end the regeneration capabilities of the Time Lords, Braxiatel used a Time Scoop to collect the Time Lord bio-data archive (along with K9). Romana was asked to decide whether to administer the cure or let Gallifrey die and rebuild it from scratch with the bio-data archive. (AUDIO: Gallifrey)
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.
Although John Leeson has been the primary voice actor for K9 since his introduction, two other actors have voiced the character. David Brierley voiced K9 during Season 17 after Leeson chose not to return to the series (Leeson subsequently signed up again for Season 18), and Roy Skelton, better known for his work voicing Daleks, voiced the character in Destiny of the Daleks when all was required of K9 was a croaking sound due to the character contracting a form of robot laryngitis.
A. The K9track.com dedicated servers are located in a state-of-the-art datacenter, which provide biometric access controls, constant surveillance, redundant power feeds and generators, robust fire suppression, and carefully monitored climate control to protect the servers that store your departments data. All information travelling between your browser and K9track.com is protected from eavesdroppers with 256- bit SSL encryption. The lock icon in your browser lets you verify that you aren't talking to a phishing site impersonating K9track.com and that your data is secure in transit.
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)
During Romana's Presidency of Gallifrey, Leela became her bodyguard, and the two K9 units were forced to work together, not always amicably. After Matthias had replaced Romana as President, he nominated her to undertake a mission to find a cure for the Free Time virus, to be followed by exile. K9 opted to remain in the employ of Matthias, fighting the infection on Gallifrey. However, Braxiatel and K9 had planned another operation. Realising that the only cure to the virus was to end the regeneration capabilities of the Time Lords, Braxiatel used a Time Scoop to collect the Time Lord bio-data archive (along with K9). Romana was asked to decide whether to administer the cure or let Gallifrey die and rebuild it from scratch with the bio-data archive. (AUDIO: Gallifrey)
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).
In the spin-off media, K9 Mark II remained Romana's faithful companion for many years. In the early 2000s, John Leeson and Lalla Ward featured in a series of audio plays produced by BBV as K9 and "The Mistress", detailing these characters' adventures in a parallel universe. As neither Romana nor E-Space could be licensed, the aliases of the Mistress and the "pocket universe" were used instead.
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