Gammon began his career in the sixties on television, usually playing henchmen on Bonanza, Batman, Felony Squad, Gunsmoke, and The Wild Wild West. His film debut was in Cool Hand Luke (1967), uncredited as prisoner Sleepy. Similarly earthy roles followed in dozens of movies including A Man Called Horse, Macho Callahan, Clint Eastwood's Any Which Way You Can (as the bartender) and Urban Cowboy (mechanical bull operator Steve Strange).