Robert Downey Jr. was impressed by Cillian Murphy's 'commitment' to lead role in Oppenheimer

Robert Downey Jr. was impressed by how committed Cillian Murphy was to the lead role in Oppenheimer.

In an interview with People, the Iron Man star praised the Peaky Blinders actor for the sacrifices he made to play the father of the atomic bomb, J. Robert Oppenheimer.

"I have never witnessed a greater sacrifice by a lead actor in my career," he gushed, adding that he was impressed by Murphy's "commitment" to starring in Christopher Nolan's biographical drama.

Giving an example of his dedication to the task, Downey Jr. recalled how Murphy often turned down opportunities to hang out with his co-stars, such as Emily Blunt and Matt Damon, because he had to stay focused on the job.

"He knew it was going to be a behemoth ask when Chris called him. But I think he also had the humility that is required to survive playing a role like this," Downey Jr. continued. "We'd be like, 'Hey, we got a three-day weekend. Maybe we'll go antiquing in Santa Fe. What are you going to do?' 'Oh, I have to learn 30,000 words of Dutch. Have a nice time.' But that's the nature of the ask."

Florence Pugh, who plays Oppenheimer's love interest Jean Tatlock in the movie, called working with the Irish actor "truly one of the best experiences" she's had during her career.

"Working with him was hugely impressive," she praised. "Every single day he shows up knowing every single possible way, intonation, inflection of how to bring this character to life. That was hugely impressive to me. There's a reason why he is one of the greats."

Oppenheimer is showing in cinemas now.