Jon Hamm -- Gregory Peck
Don's the hardest to cast, because Hamm so completely owns the role. William Holden could play a blank slate, then add on a cynical edge — perfect for Don. And Laurence Harvey might have captured Don's cold heart. But Peck (right), if he could hide his heart? I gotta go with him, not least of all because comic Jimmy Barrett once snidely called Don "The Man in the Gray Flannel Suit."