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)
Either Inspector Thorne or Lomax found out about K9's regeneration unit and decided to acquire it. Thorne joined forces with Freddie Maxwell, owner of Crashclub involving old robots being made to fight. K9 went undercover as a gladiator and made friends with the robot clowns Chuckles and Boris. He was called to fight the Pain-Maker, who was laced with the explosive solarmite. When he was set to self-destruct, K9 detected this and fled the explosion. (TV: Robot Gladiators) To regain his memory and find out his connection to the STM, K9's archive was scrambled. Directives from the STM almost caused him to self-destruct and lose all his memory. However, with Gryffen and Starkey's help he overrode the directives. (TV: Mind Snap) He helped Gryffen find the STM's temporal stabiliser from the fallen angel crash site in Canada, where it was revealed to be Korven technology. (TV: Angel of the North) He stopped haywire CCPCs when The Last Precinct's plan backfired. (TV: The Last Precinct)
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)
While caught up in a Time war between the past and the future on the planet Aoris, K9 was forced to spend a thousand years hidden on the planet, setting himself up as 'the great Machina' so that he could found a cult that would aid the Doctor and Romana in bringing the war to an end, hiding behind a fake computer with a version of the TARDIS until he could return to the Doctor and Romana once the war ended (AUDIO: The Paradox Planet, Legacy of Death).
Within the series' narrative, K9 is a robot dog acquired by Doctor Who's title character in the 1977 serial The Invisible Enemy. The first two incarnations of the character travelled alongside the Fourth Doctor (portrayed by Tom Baker) until 1981. In these stories, K9 proved useful for the powerful laser weapon concealed in his nose, his encyclopaedic knowledge and his vast computer intelligence. By 1981, each of the two models of K9 which travelled alongside the Doctor had been left with one of the Doctor's female companions. The character subsequently transitioned into spin-off territory. Producers hoped K9's popularity with children would launch the series K9 and Company, led by actress Elisabeth Sladen in the role of companion Sarah Jane Smith alongside a new K9. In 2006, K9 reappeared in the revived series of Doctor Who. Although the character's appearances in the 2007 spin-off The Sarah Jane Adventures were hampered by the concurrent development of the K9 spin-off, the character began to appear full-time in both K9 and The Sarah Jane Adventures, depicting adventures of the original K9 Mark I and of Mark IV, respectively.