For the role of Dr. Emilio Lizardo, the studio wanted to cast an unknown actor, but Mac Rauch had written the role with John Lithgow in mind. Like Weller, Lithgow was not sure about the character, but Richter convinced him by "claiming what a real feast for an actor this wonderful Jekyll and Hyde character was", Lithgow later said. He told an interviewer, "I have had roles where I came very close to going over the top. In Twilight Zone I almost went over the top several times. But this role is completely over the top. It makes the role in Twilight Zone seem like a model of restraint. I do it in a wild, red fright wig and rotten false teeth with a thick Italian accent. It's wild." For Lizardo's accent, Lithgow spent time with an Italian tailor at MGM and recorded his voice (film credit to "Roberto Terminelli: John Lithgow's dialect coach"). Lithgow changed his walk to that of an "old crab, because my alien metabolism is supposed to be messed up". He said of his character, "playing Lizardo felt like playing the madman in The Cabinet of Dr. Caligari."