The unit was particularly associated with Romana, having served both Romana I and Romana II. Indeed, he stopped travelling with the Doctor at the same time as the second Romana, with whom he remained in E-Space in order to assist with the liberation of the Tharil species. When Romana returned into N-Space, K9 joined her on Gallifrey. Once on the Time Lords' homeworld, he continued to serve Romana as she ascended to the post of Lady President of the High Council. (AUDIO: Weapon of Choice, et al)