a real world point of view
Valentine Dyall (7 May 1908-24 June 1985) played the Black Guardian in the Doctor Who stories The Armageddon Factor, Mawdryn Undead, Terminus and Enlightenment. Shortly before his death he also recorded the voice of Slarn for the radio play AUDIO: Slipback, which was broadcast after his death. He was one of the few actors considered for the role of the Second Doctor; Dyall, like the other actors, declined the offer to play the role because he didn't want to commit to a long-running role.
- Internet Movie Database at the