When you're making a film about someone as universally loved as Bob Marley, the weight of responsibility hangs heavy. 

With "Bob Marley: One Love" hitting cinemas around the world next week, director Reinaldo Marcus Green admitted he hesitated about taking on the biopic of the reggae legend -- a project that has previously defeated both Martin Scorsese and Oliver Stone. 

"The responsiblity was so large that I thought it was crazy to do this," said Green, whose previous film was "King Richard", starring Will Smith as the father of tennis stars Venus and Serena Williams. 

"But we had our world premier in Jamaica and that was a huge sigh of relief," he told AFP. 

"The Jamaican people are hard -- they are like, 'Don't mess with Bob!' -- but luckily they gave us the seal of approval."

The film focuses on a particularly rich creative period between 1976 and 1978 when Marley released the album "Exodus" that made him a global star, but also suffered an attempted assassination and discovered the cancer that would soon after claim his life at just 36. 

It was co-produced by his widow Rita Marley and their children Ziggy and Cedella -- as well as a certain Brad Pitt. 

It was Ziggy who approved British actor Kingsley Ben-Adir to play his father. 

Ben-Adir has already played two other towering historical figures: Malcolm X (in "One Night in Miami") and Barack Obama ("The Comey Rule"). 

But this has been another level for the 37-year-old actor, with his face on billboards all over the planet. 

"It's not my face I see on those posters. It's the good will and the love that Bob has around the world," he told AFP. "Bob has this power."

Ben-Adir learned to sing for the role and his voice is mixed with recordings of Marley through the film. 

The challenge was keeping up the intensity: "You never see Bob doing half-energy, it's always full," he said.

'Wasn't perfect'

The film takes pains to show all sides of Marley, who had a reputation among friends and family for being tough (they nicknamed him "The General"), competitive and "inhumanly determined", but also sweetly innocent like a little boy, Ben-Adir said.

"Everyone has an idea of Bob as a nice happy guy, but no -- he wasn't perfect," he added. "But his mission was perfect, and his music... there's nothing like it."

The family has not shied away from showing difficult moments, including a bruising argument in which Rita reminds Marley of how much she has done to build his career.

"That scene took a lot of private work with the family," Ben-Adir said. "I have so much respect for them for their bravery to share that."

Green said it was crucial to show how Rita introduced Marley to his Rastafarian religion, and guided his career and music. 

"Rita gave him a sense of purpose. He was from Trenchtown -- easy to fall victim to the streets," the director said. 

"Through music and Rastafarianism he was able to gift us his music, and Rita is responsible for that introduction to that deep faith."