Christopher Nolan cast Robert Downey Jr to show MCU fans that he’s ‘one of our great actors’

Christopher Nolan has revealed why he wanted Robert Downey Jr. in “Oppenheimer.”

The blockbuster, set to open July 21, dives deep into the life of theoretical physicist J. Robert Oppenheimer as he grapples with the enormous implications and ultimate reality of the Manhattan Project and creating nuclear weapons.

Nolan uses alternating timelines, one filmed in color that focuses on the title character and the other in black and white and focusing on Lewis Strauss, the chairman of the Atomic Energy Commission. “They had a Mozart–Salieri relationship, characterized by slights and pride,” Nolan told Kenneth Turan, longtime Times movie critic. “They were two larger-than-life characters.”

The film’s script is based on Kai Bird and Martin J. Sherwin’s 2005 “American Prometheus,” the Pulitzer Prize-winning Oppenheimer biography. After “months and months” of staring at the biography’s cover, which features Alfred Eisenstaedt’s portrait of the notorious man behind the bomb, Nolan realized that Cillian Murphy — “one of the best actors of his generation” — was staring back at him.

Murphy acted in five of Nolan’s previous films, including all three of the Dark Knight Batman epics. But who would be Nolan’s Strauss?

According to Nolan, Oppenheimer was the most important person who ever lived. So Strauss’ stature was also significant, and finding the right actor was crucial. Nolan landed on the former “Iron Man,” and noted that, although Downey is a huge star, Marvel Cinematic Universe fans probably have not yet seen him in full form.

“He’s one of our great actors, and though a generation of kids know what a great movie star he is, they’ve not seen his subtlety and brilliance,” Nolan told Turan.

“I wanted to get him to do something completely different, to lose himself in another human being. When was the last time we’ve seen that? ‘Chaplin’? Directors are very aware of how talented Downey is, but because of his incredible energy that can punch through the screen, finding the right thing for him is difficult.”

In a recent interview with Extra, Downey admitted Murphy had embodied the character of Oppenheimer in such a way that “you can’t help but feel a little bit iced out by it.”

“Cillian is so warm and nice and inviting, but then we’d roll and I’d feel like he was looking through me like I didn’t exist. And I was like, ‘That sucks,’” Downey joked. “And I can only imagine there was a lot of people who felt that way. Lewis Strauss was in a position to do something about it. I don’t know how culpable he was for that, but it is a story of how small imagined slights between important people can have big impact.”

Murphy echoed Downey and said, “And that’s the beauty of this story. It’s, you know, this tiny story in one way between these two men and this ginormous story about life and death.”

Read Turan’s full feature on Nolan here.