According to McDiarmid, he has casting director Mary Selway to thank for his most famous film role. McDiarmid explained: "[She] had seen me in a play, playing the aging, aged Howard Hughes [...] in the great Sam Shepard's play 'Seduced.' And so she said to George, 'This guy, he's relatively young, 37, who's probably going to be convincing as this old person, you know, 120.'"