Robert Downey Jr. has praised his co-actor Cillian Murphy for his efforts behind playing the  titular role in Christopher Nolan film Oppenheimer.

Murphy, who set the bar so high  with his stellar  performance  in the leading role of J. Robert Oppenheimer, has received acknowledgement for his hard work from the Iron Man actor.

In an exclusive conversation with PEOPLE, Downey Jr. gushed over the Peaky Blinders actor for his phenomenal performance in the movie.

“I have never witnessed a greater sacrifice by a lead actor in my career,” said the 58-year-old actor.

Downey Jr. continued, “he knew it was going to be a behemoth ask when Chris called him.”

The Sherlock Holmes actor added, “but I think he also had the humility that is required to survive playing a role like this. 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.”

Oppenheimer is reportedly one of Nolan's quickest film to wind up, as it was finished in only 57 days, with the Dunkirk actor featured in nearly every scene.

 It is pertinent to note, the 47-year-old actor went above and beyond for the character of Oppenheimer, he had also lost weight for the role.

Oppenheimer is the real life story of  the  theoretical physicist J. Robert Oppenheimer, known as the father of the atomic bomb.

He was tasked to lead the infamous Manhattan Project, carried out  to create the first ever atomic bomb.

 In Oppenheimer, Downey Jr. plays Lewis Strauss, chairman of the Atomic Energy Commission.