Robert Downey Jr. praises ‘Oppenheimer’ co-star Cillian Murphy: ‘I have never witnessed a greater sacrifice’

Robert Downey Jr. says he’s “never witnessed a greater sacrifice by a lead actor” than his “Oppenheimer” co-star Cillian Murphy.

Murphy stars as J. Robert Oppenheimer, the father of the atomic bomb, in the Christopher Nolan-directed three-hour blockbuster.

The film looks back at the development of the bomb, which was later dropped on both Hiroshima and Nagasaki, Japan, bringing an end to World War II.

For his part, Downey Jr., 58, plays Lewis Strauss, chairman of the Atomic Energy Commission.

“I have never witnessed a greater sacrifice by a lead actor in my career,” he told People of Murphy’s performance.

“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,” he explained.

“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.”

Elsewhere, co-star Florence Pugh, 27, who stars as Jean Tatlock, one of Oppenheimer’s significant love interests in the film, echoed Downey Jr.’s praise of Murphy.

“Chris had one of the most incredible leads in Cillian,” she told the outlet. “He is an actor that I have been watching for quite some time and have been desperate to work with for ages. You’d have to be mad to say no. It was truly one of the best experiences that I’ve had.”

“Working with him was hugely impressive,” she went on. “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.”

Murphy’s commitment to the role included following a very restrictive diet to closer resemble Oppenheimer.

According to co-star Emily Blunt, 40, who played Oppenheimer’s wife Kitty in the film, Murphy achieved the look by scarcely consuming food.

“He had such a monumental undertaking,” she told Extra earlier this month. “And he could only eat, like, an almond every day. He was so emaciated.”

The “Peaky Blinders” alum also discussed his weight loss for the role in a May interview with the New York Times.

“I love acting with my body, and Oppenheimer had a very distinct physicality and silhouette, which I wanted to get right,” he said. “I had to lose quite a bit of weight, and we worked with the costume and tailoring; he was very slim, almost emaciated, existed on martinis and cigarettes.”