Original Appearances: Doctor Who, introduced in 1977.
Other Appearances: K-9 and Company, The Sarah Jane Adventures, K-9, as well as a multitude of toys and other Doctor Who memorabilia.
Biography: There have been several K-9s in the Doctor Who saga, all robotic dogs. The first K-9, Mark I, appeared in the serial The Invisible Enemy as the creation of Professor Marius in the year 5000. K-9 traveled with the fourth Doctor and Leela until The Invasion of Time, when K-9 decides to stay on Gallifrey with Leela. It is this version that is supposed to be the star of the TV series K-9, although it is apparently considered a bit noncanonical.
The Mark II K-9 first appears in The Ribos Operation immediately, and this version lasted from 1978 to 1981, when he was severely damaged. The Mark II K-9 stayed with Romana when she left the Doctor.
The Mark III K-9 first appeared in the spin-off series K-9 and Company, presented to former Doctor companion Sarah Jane Smith, and the two have their own adventures, as well as cameoing in the 1983 The Five Doctors. The final appearance of Mark III was in the 2006 episode School Reunion, and he's fallen into disrepair, and sacrifices his life to stop the alien Krillitane. The Doctor presents Sarah Jane with a new K-9 at the end of the episode, rebuilt with the same mind and memories.
This Mark IV K-9 appears briefly in the spin-off series The Sarah Jane Adventures in the episode “Invasion of the Bane,” and then only appearing sporadically. He later appears in the 2008 season of Doctor Who with new abilities, and then returning to The Sarah Jane Adventures in the 2009 series, staying until 2010, then reappearing in the fourth series' finale episode.
Powers: Various powers the K-9 models exhibited included a head-up display, ability to fly, laser weapons, and probably other abilities as needed by the writers of the various series.
Group Affiliation: Robotic companion to the Doctor and a few companions.
Miscellaneous: The series K-9 was not produced by the BBC, as they decided to focus on their own Doctor Who spin-off, Torchwood. This series was much more aimed at children than Doctor Who was, and sported a much more sleek and curved design as its predecessors.