The screenplay is written by Christina Hodson (“Birds of Prey”) from characters created by Gardner Fox and Harry Lampert. Ezra Miller’s Barry Allen travels back in time to stop his mother’s murder, generating unintended consequences. Joining the cast are Ben Affleck as Bruce Wayne aka Batman; Michael Keaton also as Bruce Wayne aka Batman in an older, alternate universe; Sasha Calle as the Kryptonian Supergirl; and Kiersey Clemons as journalist Iris West, aka Barry’s love interest. The movie finds the eponymous superhero journeying through the multiverse, which is why both Keaton and Ben Affleck will appear as iterations of Batman in the same movie. Keaton told The Hollywood Reporter that he decided to return to the Batman character because he always wanted another chance to “go back and nail that motherfucker…so I thought, ‘Well, now that they’re asking me, let me see if I can pull that off.’” However, making sense of the multiverse was a challenge.

“I had to read it more than three times to go, ‘Wait, how does this work?’” Keaton said. “They had to explain that to me several times. By the way, I’m not being arrogant, I hope, about this. I don’t say it like, ‘I’m too groovy.’ I’m stupid. There’s a lot of things I don’t know about. And so, I don’t know, I just kind of figured it out, but this was different.” Keaton continued, “What’s really interesting is how much more I got [Batman] when I went back and did him. I get this on a whole other level now. I totally respect it. I respect what people are trying to make. I never looked at it like, ‘Oh, this is just a silly thing.’ It was not a silly thing when I did Batman. But it has become a giant thing, culturally. It’s iconic. So I have even more respect for it because what do I know? This is a big deal in the world to people. You’ve got to honor that and be respectful of that. Even I go, ‘Jesus, this is huge.’“

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