Harris has the rare distinction of appearing as different characters in all three films of the original Star Wars trilogy (as well as as the first prequel, The Phantom Menace), as well as playing a Stormtrooper in all three films. Harris also got to play the role of a vervoid, a plant-like humanoid alien, over the course of several Doctor Who episodes. When the Star Wars prequel trilogy finally rolled around, Harris returned to double as the actor Terence Stamp, who played Supreme Chancellor Finis Valorum.
Though his acting career mainly comprised of playing an extra, Harris managed to do it in some of the biggest franchises and films in Hollywood. His IMDB page also lists minor credits for Flash Gordon, The Shining, Superman, and A Clockwork Orange.