“[Joaquin] never liked saying the name Thomas Wayne,” Phillips said. “It would have been easier for him if the movie was called 'Arthur' and had nothing to do with any of that stuff. But in the long run, I think he got it and appreciated it.”
Actor Brett Cullen stars in “Joker” as Thomas Wayne. By writing Thomas Wayne into the script, Phillips and co-screenwriter Scott Silver keep “Joker” tied to the mythology of the comic book despite telling a wholly original story about Arthur Fleck, an aspiring standup comedian and clown for hire who descends into the Joker. Dante Pereira-Olson appears briefly in the movie as Bruce Wayne, suggesting Batman could one day exist in the “Joker” mythology.
Phoenix reveals to The New York Times that he and Phoenix also had “fruitful disagreements” over the physical transformation that would be required to play Arthur Fleck/Joker. Both men agreed Phoenix should undergo a “drastic weight change,” but Phoenix wanted to put on the pounds and not lose them. After slimming down for roles in the past, Phoenix told Phillips he did not want to do it again.
“It's a horrible way to live,” Phoenix said. “I think [Arthur] should be kind of heavy. Todd was like, 'I think you should do the real thin person.'”