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.
Despite his expertise, Sebastian can be identified by his weak eyes - he blinks excessively when exposed to bright light.
See also Rudolph T. Sebastian.