During his career Sebastian has impersonated Senator Farfan, tennis champion Fred Giles, TV host Johnny Carson (for two weeks!), newscaster Chet Huntley (or his on-air partner David Brinkley, they are still not sure which) and even Maxwell Smart's Aunt Rose. Sebastian is KAOS's master executioner, so dangerous he is considered a "101" - shoot on recognition. Smart encounters Sebastian when he transforms himself into a duplicate of the Chief to gain access to Max's apartment in order to eliminate defector Tanya Lupescu before she can reveal vital information.