After the death of his Tony Stark in 2019’s Avengers: Endgame, Robert Downey, Jr. explains he was concerned about his acting muscles after they spent so many years, metaphorically, in an Iron Man suit.

“You start to wonder if a muscle you have hasn’t atrophied,” he tells The New York Times Magazine, explaining his turn in Oppenheimer for director Christopher Nolan was the ideal way to stretch.

“I knew there was a point where Chris Nolan was endorsing, let’s work those other muscles, but let’s do it while rendering you devoid of your usual go-to things,” which Downey defined as “the fast-talking, charming, unpredictable…” characters from previous films.

In Oppenheimer, Downey plays the former chairman of the Atomic Energy Commission Lewis Strauss, who butted heads in real life — as he does onscreen — with J. Robert Oppenheimer, played by Cillian Murphy.

RDJ says, “I don’t know why I can relate to Lewis Strauss so much, but I felt like I was meant to play this role, and I knew I’d be in capable hands.”

For his part, Nolan recently told the Los Angeles Times of Downey, “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?”

He adds, “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.”

The actor tells The New York Times Magazine of Oppenheimer, “Coming from that other place…the box-office-weekend-dominating place, then going into this spot now where I’m happy that I’m in this quality product — I’m happy that I regained my connection with a more purist approach to making movies.”

Oppenheimer opens July 21.

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