Although many doppelgangers are impossible to tell apart, you’d have no problem with Red Dwarf’s Rimmer and his heroic counterpart Commander Arnold Judas Rimmer. One’s a snivelling egocentric git with a large H on his forehead, the other’s a modest hero who was kept back a year at school when he was seven years old and likes to use the phrase, “Smoke me a kipper, I’ll be back for breakfast!”
Ace made his first appearance in Season 4’s ‘Dimension Jump’, but proved so popular that he occasionally appeared in future seasons.