When an actor plays more than one role in a movie, it’s not because they’re trying to save on salaries; it’s to show off their acting skills. The first such actor that comes to mind is Peter Sellers, in my case, but there are plenty of movies with a lead actor playing multiple roles. There are probably some that you haven’t seen, like Kind Hearts and Coronets.
Before he was knighted, and before he donned the robes to play the legendary Obi-Wan Kenobi, Alec Guinness played now fewer than eight (!) roles in King Hearts and Coronets, including the role of a woman. He was only 35 when he played all these roles, and I guess you could say he played 8.5 roles: he sat for a painting of one of his character’s ancestors, too. Almost everyone in our generation thinks of Guinness as Obi-Wan only, and I think that’s a disservice. The man was mad talented.
See the rest of the list of actors who’ve played more than one role in a movie at TVOM.