K9 Mark I

K-9 Mark I was built by Professor Marius to accompany and assist him in his work at the Bi-Al Foundation. He served as the template for all future versions of K-9.

He joined the Doctor and Leela (DW: The Invisible Enemy), but left with Leela when she decided to remain on Gallifrey with her new lover, Andred. (DW: The Invasion of Time) Later, it is believed that the Time Lords assigned K-9 the command of a space vessel called K-NEL and gave him occasional assignments. (The Adventures of K9)

It is unknown if he survived the Time War as Gallifrey was destroyed. his mistress Leela survived though. (BFA: The Catalyst)