Christopher Nolan has begun filming his atomic bomb drama “Oppenheimer,” starring Cillian Murphy in the eponymous role of Manhattan Project leader J. Robert Oppenheimer. Murphy is leading his first Nolan tentpole after playing supporting roles in five of the director’s movies (three “Dark Knight” films, “Inception” and “Dunkirk”). When it came time to prepping for “Oppenheimer,” Murphy skipped over all the mechanics of what makes an atom bomb and instead focused on the man himself.

“[I prepped by doing] an awful lot of reading,” Murphy recently told The Guardian. “I’m interested in the man and what [inventing the atomic bomb] does to the individual. The mechanics of it, that’s not really for me — I don’t have the intellectual capability to understand them, but these contradictory characters are fascinating.”

Murphy drew a connection between the contradictory nature of Oppenheimer and that of his “Peaky Blinders” character Tommy Shelby. The actor said, “People identify with that, because we all walk around with these contradictory ideas coexisting in our heads.”

Nolan’s “Oppenheimer” script is based on Kai Bird and Martin Sherwin’s biography “American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer,” which was part of Murphy’s reading list during prep. Although the film marks Murphy’s first leading Nolan role, he said the size of the role means nothing when it comes to the “Dunkirk” and “Tenet” filmmaker.

“I’ll always turn up for Chris, whatever the size of the part,” Murphy said. “Chris will call me up and I’m there. Isn’t it wonderful that filmmakers are still making challenging, demanding films within the studio system, shot on film? I think he’s flying the flag. Him, Paul Thomas Anderson and Quentin Tarantino are fantastic filmmakers making interesting work on a massive scale.”

Nolan has assembled his most star-studded cast to date for “Oppenheimer.” Joining Murphy in the movie are Emily Blunt as biologist and botanist Katherine “Kitty” Oppenheimer, Matt Damon as Manhattan Project director Gen. Leslie Groves Jr. and Robert Downey Jr. as Lewis Strauss, a founding commissioner of the U.S. Atomic Energy Commission. Florence Pugh plays psychiatrist Jean Tatlock, Benny Safdie portrays theoretical physicist Edward Teller, Michael Angarano plays Robert Serber and Josh Hartnett portrays pioneering American nuclear scientist Ernest Lawrence. “Oppenheimer” also stars Rami Malek, Dane DeHaan, Dylan Arnold , David Krumholtz, Alden Ehrenreich and Matthew Modine.

Universal Pictures will distribute “Oppenheimer” theatrically worldwide and will release the film in North American theaters on July 21, 2023.