Robert Downey Jr. ‘Never Witnessed a Greater Sacrifice’ by an Actor Than Cillian Murphy’s in Oppenheimer

Robert Downey Jr. has praised Oppenheimer co-star Cillian Murphy for his extraordinary commitment to his craft, saying he has “never witnessed a greater sacrifice by a lead actor” in his entire career.

Murphy plays J. Robert Oppenheimer, the theoretical physicist commonly regarded as one of the “fathers of the atomic bomb”, in Christopher Nolan’s new biopic. Downey Jr. told People magazine that Murphy’s role was no small undertaking, but as an actor, he had the “humility” to deliver a truly transformative performance.

“I have never witnessed a greater sacrifice by a lead actor in my career,” Downey Jr. said. “He knew it was going to be a behemoth ask when Chris [Nolan] called him. But I think he also had the humility that is required to survive playing a role like this.”

Downey Jr., who plays Atomic Energy Commission chairman Lewis Strauss in the movie, shared a brief but illustrative anecdote to elaborate further on the qualities Murphy brought to the role, specifically his dedication and the time he personally invested in perfecting his portrayal of the movie’s titular physicist.

“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,’ ” Downey Jr. recalled before adding, “But that’s the nature of the ask.”

Murphy’s devotion to the role included following an extremely restrictive diet in order to become the “emaciated” Oppenheimer. His co-star Emily Blunt, who plays his onscreen wife, told Extra that Murphy “could only eat, like, an almond every day” as part of a “monumental undertaking” to transform into the character.

Separately, Murphy told 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. 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.”

Oppenheimer is an adaptation of the 2005 Pulitzer Prize-winning book, American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer, which chronicles the life of the famed nuclear physicist. The movie explores his work on the Manhattan Project and his role in developing the atomic bomb.

Nolan’s big-screen biopic hit theaters on July 21 as one part of the ‘Barbenheimer’ phenomenon. IGN’s review of Oppenheimer described it as a “jolting thriller” that offers “a disturbing, mesmerizing vision of what humanity is capable of bringing upon itself, both through its innovation and through its capacity to justify any atrocity”.

Adele Ankers-Range is a freelance entertainment writer for IGN. Follow her on Twitter.