'Batman' (TV series) (1966-1968)
Cesar Romero -- the mustached Joker.
Romero appeared in 18 episodes of the campy 1960s series that removed all of Joker's homicidal streak and turned him into a cackling prankster. This was a reflection of the way the character was portrayed in the comics at the time, where superheroes were treated with little seriousness.
Romero refused to shave his mustache for the role, and it can still be seen beneath his white makeup in close-ups.