The actor recalls talking to Chadwick about the role while he was filming "Pacific Rim" in Toronto. "He sat with me, watched me work and we talked and talked," said Elba in his strong British working class accent. "I started to warm up to the idea. But I was really scared. I thought, 'Oh my God, if I mess this up, what the hell? I'll never work again.' " 

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A lot of his fears were laid to rest when he met Naomie Harris, who plays Mandela's second wife, Winnie, the naïve young social worker who transforms into a defiant militant. "The on-screen chemistry was amazing," said Elba. "I am looking at Winnie and Nelson, I am not looking at Naomie and I. The love feels so real."

Though he never got to meet the 95-year-old Mandela, who has had serious health issues, Elba has become close to his family. At the premiere this month in South Africa, Mandela's daughter Zinzdi even said to him, "Come here, Dad," so they could pose together for photos.

Elba insisted that he spend a night in one of the dehumanizing small cells on Robben Island, where Mandela spent 18 years in prison. It is now a museum.

The officials turned him down several times. Frustrated, Elba even contemplated getting into a brawl in a bar so he could spend the night in jail. But finally, the Robben Island officials allowed him to stay in a "punishment" cell. 

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"When you are locked in the room you are powerless," said Elba. "I was lucky I only had 24 hours. But it just put it into context and what his frame of mind was to have endured for that long of time."

Chadwick said he always knew that Elba would be "brilliant" as the young Mandela. "It was the older, more recognizable Mandela that was the challenge that we had to catch."

Because the indie film didn't have deep financial pockets,  "we had to be canny with our resources ... we had to shoot totally out of sequence," said Chadwick.

In fact, in one day Elba had to do a quick transformation from a 40-year-old Mandela to the elderly man in his 70s.

"His walk and his body language was breathtaking," said Chadwick. "He became Mandela."

susan.king@latimes.com