Kryten

... first appeared as a guest character in Series 2, when he was played by David Ross. From Series 3 he became a regular character and was played by Robert Llewellyn.

He was rescued by the Red Dwarf crew from the crashed spaceship Nova 5 in the first episode of Series 2, having spent countless years continuing to serve the ship's crew without realising they had been long dead. Bound by his "behavioural protocols", he is taught independent thinking by Lister and leaves the Red Dwarf on a "space bike" to enjoy his newfound freedom. Between series 2 and 3 he is rescued by the crew after his space bike crashes on an asteroid. He becomes part of the Red Dwarf crew, and Lister's best friend.