Robert Downey Jr. Says Cillian Murphy Made Biggest Sacrifice of Any Actor He's Ever Seen for 'Oppenheimer' (Exclusive)

"I have never witnessed a greater sacrifice by a lead actor in my career," Robert Downey Jr. tells PEOPLE of his "Oppenheimer" costar

Transcript

00:00 Robert Downey Jr. was relatably floored by Cillian Murphy's transformative performance

00:05 as J. Robert Oppenheimer in Christopher Nolan's new epic film.

00:09 The world will remember this day.

00:14 The movie revolves around Oppenheimer, an American physicist who led the U.S. effort

00:18 to create an atomic bomb during World War II.

00:22 And Downey praised his co-star, telling People, quote, "I've never witnessed a greater sacrifice

00:27 by a lead actor in my career."

00:29 In the movie, Downey plays Atomic Energy Commission Chairman Louis Strauss, and he says Murphy's

00:33 commitment to the massive undertaking left him impressed.

00:37 Downey explains that Murphy knew it was going to be a behemoth ask when Nolan called him

00:41 for the role, but he also had the humility a role like this required.

00:45 The actor recalls situations where they had a three-day weekend and would make plans to

00:49 go places, but Murphy wouldn't join because he had 30,000 words of Dutch to learn.

00:54 Florence Pugh, who shares most of her scenes with Murphy as one of the major loves of Oppenheimer's

00:59 life, Jean Tadlock, echoed Downey's praise.

01:02 She called working with Murphy one of the best experiences she's ever had and called

01:07 Murphy himself one of the greats.

01:09 Pugh lauded his attention to detail, adding that he knew every single possible way, intonation

01:14 and inflection of how to bring this character to life.

01:18 Murphy's commitment to the role included following a very restrictive diet to more closely resemble

01:23 Oppenheimer.

01:24 The Irish actor addressed his dramatic weight loss for the role during a recent interview

01:28 with IndieWire, stressing, "I don't advise it.

01:32 Oppenheimer is in theaters now."

01:33 (upbeat music)