David Oyelowo spent many days studying Martin Luther King's vocal delivery.
"This is me being back home in the UK and wanting to represent," says David Oyelowo. Walking into a central London hotel room wearing a grey Tweed suit, Oyelowo understands that clothes indeed make the man. But then Dr Martin Luther King, jnr - the late American civil rights activist, whom the 38-year-old actor portrays in Selma - also believed it was important to look your best.
"It was a big part of who he was," he says. "He was very clear about representation and what that meant in the time in which he lived. The status quo wanted to marginalise black people and dismiss their intelligence. He was aware the platform he had would allow him to present himself as a dignified, intelligent, human being.
"The way he dressed fed into that, so for him to be shoddily dressed would fit into a narrative of 'they should be dismissed'. He and the other civil rights leaders were all very fastidious in how they presented themselves, and I am as well."
Born in Oxford to Nigerian parents, Oyelowo came to prominence in 2002 when he landed the role of MI-5 operative Danny Hunter in the first season of Spooks.
He moved to the United States around a decade ago, and appeared in films such as The Paperboy, Rise of the Planet of the Apes and Jack Reacher. Selma should be his breakthrough.
Oyelowo has been attached to the film since it was mooted in 2007. The first movie dedicated to King in the almost half-century since his death in 1968, Oyelowo has been the one constant factor in Selma's troubled development. Stephen Frears, Michael Mann, Spike Lee and Lee Daniels all failed to raise the necessary finance. Oyelowo recommended African-American director Ava DuVernay after working with her on her second feature Middle of Nowhere.
Crucially, he also convinced Oprah Winfrey to come onboard as a producer and to play the small but significant role of Annie Lee Cooper, who in the opening scene is shown forlornly trying to register to vote at a courthouse in the Alabama small town from which the film takes it name.
"It's indicative of the people who have the ability to green-light films that they want to have their stories told," he says.
"That's why you have a J. Edgar Hoover movie before a Martin Luther King movie. It takes someone like Oprah to say 'you know what? I want to see a representation of my family and my history up on the big screen and I have the power and the reputation to support that'.
"I played her son in The Butler, so I told her 'we need you otherwise this film won't get made.' She agreed and, I kid you not, that was the change agent. As someone who has been on the film for 7½ years, I can tell you she was the rocket fuel we needed."
Oyelowo is almost unrecognisable as the 35-year-old Atlanta-born pastor. He is older than King was when he visited Selma in January 1965 to organise the voting rights protest that led to the pivotal march on the Alabama state capital of Montgomery.
"The amazing thing about playing someone like him is that there's a lot of footage and recordings," he says. "There's also a copious amount of books, which is a blessing and also a curse because everyone feels they already know who he is.
"So if you're going to play him, you've got a lot of people to please. But you have to put that aside and find the human being behind all of that. I did as much as I could to be like him. He was bigger than me so I had to gain a bunch of weight."
He also closely studied King's vocal mannerisms, staying in character throughout the 32-day shoot. "People often say to me 'you're British, how did you do that?'
"But not many Americans can listen to King and say 'I've got that'. He had Atlanta in his accent, Boston was also in there because he spent his formative years studying there. Plus he had the Southern Baptist preacher element as well. And he was reacting against that sing-songy way of preaching.
"I had to deconstruct all those things to understand where those sounds were coming from. Then once you had it, you let it go because if you're just there trying to hit those beats, it wouldn't feel lived in, it wouldn't feel like you're looking at a person."
Disappointingly only nominated for Best Picture and Best Original Song at the forthcoming Academy Awards, Selma has been a success with cinemagoers. It grossed US$5 million in its first 24 hours alone when it opened in the US, appropriately on Martin Luther King Day last month.
"Films like this just don't get made because of the notion, the theory, the lie that films with a black protagonist don't travel beyond America," says Oyelowo.
"But I'm sitting here talking about a film about Martin Luther King that is being distributed internationally and we had a big red-carpet premiere here in London. That didn't happen with these kinds of films until 12 Years a Slave and The Butler, which were critically acclaimed and did close to US$200 million at the box office.
"But both of those films were about subservient characters. What I haven't seen since Spike Lee fought so hard to make Malcolm X is a movie about a black character who is a leader who challenges the status quo, who is also doing the business that we're doing.
"That, to me, is an indication of progress."
Selma is screening in cinemas now.