Someday K9 saved the people at the Aurora from being killed by a Federation war cruiser. (PROSE: Peaceniks) When K9 wanted to help a space ship navigating back to New Earth he met Interstitials. These creatures were living in a state relating to the space or time between things. K9 helped them pass into another existence where it was better for them. (PROSE: Interstitials)
Jealous, Possessive by Paul Magrs, the "Scorpio" story in Big Finish's anthology Short Trips: Zodiac features K9 Mark I and Mark II relaying their exploits to each other, and their veiled put-downs to each other reveal that each considers the other to be the "inferior" version. This attitude is also occasionally hinted at in the way the two units refer to each other in the Gallifrey audio 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.
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)
On August 1, 2016, Blue Coat, Inc. (K9’s parent company) was acquired by cybersecurity leader Symantec™.  As can be imagined Blue Coat and Symantec had a handful of similar products and unfortunately, it didn’t make sense to maintain two competing products. it was decided to “end-of-life” K9 Web Protection and focus corporate and customer attention on Symantec’s line of Norton™ products.

After Mark I sacrificed himself to destroy the Jixen warriors, Starkey retrieved his regeneration unit, which quickly activated. In a blast of white light, K9 was thus reborn as a much more advanced model, though this K9 Mark Z could not access the memories of his previous self, which had been "scrambled". He stayed at the house of Alistair Gryffen, who ran tests on K9, but did not tell the Department. K9 tried to kill Starkey, as he was sprayed with Jixen genetic matter and so registered as a Jixen. Starkey convinced him that he was not an enemy and K9 gave him his dog whistle to summon him when needed. (TV: Regeneration) K9 and the team tracked down the surviving Jixen to Dauntless Prison and killed it. They also faced a Meron and freed the alien prisoners. (TV: Liberation) K9 travelled with Starkey when he was on the run from the Department and rescued Gryffen (who was kidnapped by a Korven). Gryffen later welcomed him and Starkey into his home. (TV: The Korven)
K9 Mark 2 had some obvious commonalities with the Mark I that had preceded him. However, as he had almost completely lost his personal memories, he was forced to reacquaint himself with the world around him. Toward this end, he downloaded thousands of human movies onto his memdrive, which peppered his speech with 20th and 21st century English colloquialisms that his "brothers" did not typically employ. (TV: Alien Avatar) Despite his negative opinions of emotions, (TV: Mutant Copper) he asked questions about some, such as fear (TV: Fear Itself) and love (TV: Aeolian). He even showed some, laughing when he saved the day, feeling fear (TV: Fear Itself) and being angry. (TV: Regeneration)
Solid K9 Training has a worldwide reputation of being able to handle the most challenging dog behavior with a high degree of success, as well as starting your dog off on the right foot and preventing bad behaviors that most families struggle with. We will train your dog no matter the breed or the behavioral problems you are experiencing. The greatest gift you can offer your dog is INCLUSION in your life.
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.

After debuting in the final scene of "School Reunion" (2006), K9 Mark IV returned in spin-off series The Sarah Jane Adventures' premiere episode "Invasion of the Bane", where due to licensing issues with creator Bob Baker it is explained that K9 is sealing a black hole and can only communicate briefly and infrequently with Sarah Jane. The character makes an heroic appearance in the first series finale The Lost Boy, to do battle with rogue alien supercomputer Mr Smith (Alexander Armstrong), demonstrating new CGI teleportation and hovering features. K9 Mark IV's interfaces include at least one USB port.[2] Subsequently, the character appears briefly in the Doctor Who series four series finale "Journey's End" (2008), wherein K9 and Mr Smith assist the Doctor in returning Earth to its proper position. K9 next appears in the comedic Red Nose Day 2009 Sarah Jane mini-episode "From Raxacoricofallapatorius with Love".[3] A deal with the creators of K9 having been struck, K9 Mark IV became a regular character in The Sarah Jane Adventures in third series story, The Mad Woman in the Attic (2009), until the series four premiere The Nightmare Man (2010), where he accompanies departing series regular, Sarah Jane's adoptive son Luke Smith (Tommy Knight), to university. He appears again in series four finale, Goodbye, Sarah Jane Smith. Though he doesn't appear in the serial, it is mentioned in The Man Who Never Was (2011) that Luke invented a special dog whistle to summon him with.

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