This is a bit of a cheat since Sellers plays three roles in Stanley Kubrick's Dr. Strangelove; it has been speculated that he was once considered for a fourth, somewhere in the bomber sequence. But any two of his characters would qualify for the list, and he did receive an Oscar nomination for his troubles. First, he was the meek, English Group Capt. Lionel Mandrake, then the bald, soft-spoken American President of the United States, and finally, the mad title character, who can't seem to control the actions of his right arm. If you're going to quibble, then we can quickly substitute Sellers' dual role in Kubrick's Lolita, from two years earlier.
Did we forget any? Please leave your comments with your other favorite dual roles.