In 1985, a series of gamebooks featuring the Sixth Doctor were published by Severn House under the title Make your own adventure with Doctor Who in Britain and Find Your Fate — Doctor Who in the United States. These books were actually written by scriptwriters for the television series. Martin wrote Search for the Doctor which takes place in the mid-21st century and features K9 Mark IV being reunited with the Sixth Doctor long after Sarah's death.
K9 stayed with Leela on Gallifrey for many years. It was only after the disappearance of her Time Lord husband, Andred, that Leela and her K9 met Romana II and her K9. The two K9s did not get on well and competed. (AUDIO: Weapon of Choice) After Leela became Romana's bodyguard and after many important missions on her behalf, Leela's K9 was destroyed by an exploding bomb. Leela was heartbroken, but refused to have a duplicate unit built. (AUDIO: Imperiatrix)
With his great intelligence, he had a tendency to bore people with facts and did not stop immediately when asked, as he did to Leela on Pluto. When being told that he would have to stay behind in the TARDIS, K9 often argued, giving the Doctor reasons why he should go such as "he would be a good dog." K9 always wanted to assist the Doctor. He had great intelligence and skill at chess, claiming to be able to beat the Doctor in six moves (although this may only have been because he was programmed with all chess games since 1886). (TV: The Sun Makers, The Androids of Tara) K9 had an aggression mode. (TV: State of Decay)

During training at Master Dog Training, a K9 officer will better understand his or her dog, and the police dog will flawlessly perform its duties. During work and practice, the handler will be able to improve his or her dog’s performance, rather than ruin it by doing something incorrectly. For a K9 Police officer, we will solve any behavior problems that the dog might be displaying, and will teach the handler how to correct these problems during work. During the K9 police test, we will be teaching how to properly pass it through all the different disciplines.
Solid K9 Training, founded by award-winning, internationally-acclaimed dog trainer Jeff Gellman, is one of the nations most effective and respected dog training services providing no-nonsense, "Real World" training methods throughout New England. Serving dog owners from Hartford, CT to Boston, MA in our multifaceted, secure and 24/7 staffed Solid K9 Training Center in Providence, RI, as well as all throughout the nation with Jeff's wildly successful RV Dog Trainer Tour. We will train any dog, regardless of breed, shape, size or history. We work to fix all dog behavior issues including excessive barking, growling, snapping, nipping, dog aggression (fighting), human aggression (biting), child aggression, pulling on leash, leash aggression, leash reactivity, skateboard reactivity, resource guarding, jumping on people, fear issues, anxiety issues, separation anxiety, chewing and destroying household items, running away, not listening, door bolting, stealing food, getting into the trash, cat aggression, chasing game, and killing animals/game. We also have a renowned reputation specializing in obedience training, which includes heeling and walking properly on a leash, sit/stay, down/stay, place, recall training (come to owner), and crate training. Our Training services include Board and Train behavioral modification, 1 on 1 Training, Obedience Classes, Puppy Training programs, Boarding / Board & Play, Daycare, and many free dog training resources including Dog training advice videos, dog training webinars, and Dog Training Q and A videos on Periscope on Monday and Wednesday nights. Our behavior modification training is cutting edge, using techniques like modern low level E-collar (remote collar) training and food and clicker training. Solid K9 Training has a worldwide reputation of being able to handle the most challenging dog behaviors and often times other dog trainers will refer their more serious cases to us. For more information on our services offered, as well as free dog training tutorial videos, please see my website and other social media pages: 

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.
This K9 exhibited the ability to sense and warn others of danger. He was also more mobile than his predecessor, despite his problems with the swamps of Delta III, able to lift himself up on small support rods so that he could climb stairs (PROSE: The Shadow of Weng-Chiang, TV: The Power of Kroll, The Armageddon Factor) The Doctor often used a glib remark to disarm those who were surprised by K9's appearance, such as "They're all the rage in Trenton, New Jersey." (TV: The Stones of Blood)

On 24 October 2015, Bob Baker and Paul Tams announced the film K9: TimeQuake which is destined for cinemas in 2017 and is to feature the robot dog facing off against classic Doctor Who villain Omega in deep space. However, this did not happen leaving it unknown when the movie will be released.[4][5]. In 2018 it was confirmed TimeQuake was confirmed to still be in pre-production, with plans for a prequel TV show to establish K9 for modern audiences before the movie.
K9 Mark I, II, III, and IV addressed whoever was directing them as "Master" or "Mistress" depending upon gender, and used the formal "affirmative" and "negative" rather than "yes" and "no". They were programmed to be both loyal and logical, with a penchant for taking orders literally, almost to a fault. Their striped collars mirrored the Fourth Doctor's trademark scarf.
K9, occasionally written K-9, is the name of several fictional robotic canines (dogs, the name being a pun on the pronunciation of "canine") in the long-running British science fiction television series Doctor Who, first appearing in 1977. K9 has also been a central character in three of the series television spin-offs: the one-off K-9 and Company (1981), The Sarah Jane Adventures (2007–2011) and K-9 (2009–2010). Although not originally intended to be a recurring character in the series, K9 was kept in the show following his first appearance because he was expected to be popular with younger audiences. There have been at least four separate K9 units in the series, with the first two being companions of the Fourth Doctor. Voice actor John Leeson has provided the character's voice in most of his appearances, except during Season 17 of Doctor Who, in which David Brierley temporarily did so. The character was created by Bob Baker and Dave Martin, to whom rights to the character still belong; consequently, Baker's spin-off series K9, which is not BBC-produced, cannot directly reference events or characters from Doctor Who, though it attempts to be a part of that continuity.
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