Ask a black actor which person he would be most nervous about playing, and he may well say Nelson Mandela. That was the task facing U.S. actor Dennis Haysbert, when he accepted the role in "Goodbye Bafana", a film describing the effect Mandela had on a prison warden who guarded him for over 20 years. The movie, which premiered at the Berlin film festival on Sunday (February 11), is based on the memoirs of James Gregory, posted to watch over Mandela from the late 1960s to Mandela's release in 1990 after 27 years in jail. An emotional Haysbert told reporters after the press screening of the film that it had been an overwhelming role. "To play a man whose love for his country outweighed his love for himself, his youth, his family, the sacrifices that he made, were profoundly sad to me." "I'll say now to you what I have not said to my colleagues ... Every night I went home (during filming) I would have a glass of wine and just cry," he added, fighting back tears. Although he does not try to mimic Mandela exactly, Haysbert, best known as the president in television series "24", does seek to replicate his accent and intonation, and worked hard to make sure he was as convincing as possible. He said he read everything he could read and saw every DVD of his experiences. He said that while filming in the original places in South Africa he saw that the still had a long way to go, but that he had been left with a feeling of hope. While Gregory, who died in 2003, had no involvement in "Goodbye Bafana", his wife Gloria visited the set and helped actress Diane Kruger, who portrayed her, with her performance. "It's an incredibly complex and difficult, obviously as everyone knows, political kind of quagmire, and it goes back in the research that I did, it goes back two or three hundred years to slavery," said actor Joseph Fiennes who plays the prison guard James Gregory. "And so you have to sort of go right back to really understand the role of what one wonderful journalist called the "pale native" and that's what Gregory was, he's a pale native, he's African but not, so there's a slight schizophrenia amongst I think people of that generation, speaking from James Gregory's point of view." At the start of the film, when Gregory and his wife are sent to Robben Island where Mandela and other political prisoners were kept, the couple share the view of many white South Africans at the time that God had made them superior to blacks. Haysbert said that as a black American, he felt that south Africa had progressed further than many states in America in terms of civil rights. "You know, people are spoon-fed information, and misinformation every day, and if we don't stand up and say 'wait a minute, this sounds like crap, I can't accept this, but if you have no other recourse, no dissenting voices, nobody saying 'hey no, look at this', come out of your shell, take your head out of the sand and look at this, and that is what Mandela said, you know, that is what he did." Gradually Gregory's prejudices are challenged by Mandela's courage and love, even for those who hate him. The historical context is given through real news footage of riots and speeches from the period. "We represent real people, extraordinary people in the case of Nelson Mandela, and James Gregory as a real person, obviously you want to honour that as best you can, and I think it is a wonderful human story," said Fiennes at the movie's premiere. "So fingers crossed that they love it." The press reception to the film, one of 22 competing for the coveted Golden Bear award in Berlin, was warm. But the biggest test will come with its release in South Africa.