Mortensen plays a bodyguard to Mahershala Ali's character.
Danish-American actor Viggo Mortensen says he was nervous at first about playing a burly Italian-American bouncer from the Bronx in comedy-drama Green Book, unsure whether he could portray the character convincingly.
The 59-year-old, best known for The Lord of the Rings and Captain Fantastic, also had to gain weight for the role of Tony Lip, who is hired to drive black pianist Don Shirley, played by Oscar winner Mahershala Ali, on a concert tour of the segregated US Deep South in the early 1960s.
"I was a little nervous about taking the role," Mortensen said at the opening of the Zurich Film Festival on Thursday.
"For one thing, I'm not Italian-American. And there's a lot of good Italian-American actors," he said.
"I asked (director) Pete (Farrelly) whether he was sure and he said yes and I said 'Well, let me think about it'. So, it took me a little bit to commit, but I'm glad I did. It's a beautiful movie."
Inspired by a true story, the movie has garnered early talk of an Oscar nomination since winning the Toronto International Film Festival's People's Choice Award this month.
While Tony and Don appear to have little in common at first, friendship blossoms as they encounter prejudice as well as threats on their journey.
"The movie says to me we all have similar needs. We all have a desire, a need to be respected for who we are, wherever we're from, whatever we look like, whatever our education level is," Mortensen said. "Everybody deserves a hearing."
Green Book is directed by Peter Farrelly, who with his brother Bobby is best known for the comedies There's Something About Mary and Dumb and Dumber.
"I've been asked over the years 'Do you think you'll ever make a drama?' and I said 'Yeah, when it comes'. I never planned, OK, now I'm going to make a drama," Farrelly said at the festival opening.
"This happened to be the one... It was a no-brainer when it came. It just felt right."
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