Sophie Okonedo is still trying to figure out how she made the leap from a hooker in “Dirty Pretty Things” to the wife of a real-life hero in “Hotel Rwanda.”

“I’m not quite sure how (director) Terry George thought that part made me right for this one,” says the 36-year-old actress. “He just said that he remembered me, and then I read for it. Some weeks later I got it. It sounds quite simple, but I’m sure many things were going on in the background without me knowing. I’m sure it’s quite difficult to cast an unknown in a lead role.”

Unknown, that is, to most moviegoers but not legit audiences in London, where she has built a successful career with the Royal Shakespeare Company.

Appearing in a range of productions from “The Changeling” to “The Vagina Monologues” is one thing. Playing a key part in a riveting drama about a hotel manager (Don Cheadle) who decides to house more than 1,200 refugees where he works in the midst of genocide is quite another.

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“The biggest challenge for me was sort of de-Westernizing myself,” Okonedo says.

She was helped in that process a number of ways. First was getting to know Paul and Tatiana Rusesabagina, the husband and wife at the center of the story. Second was filming on location in South Africa. And third was working with the film’s extras, many of them refugees from Congo, Sudan, Rwanda and other countries on the continent.

“Sometimes you have to put yourself in another place, but with this film I really didn’t have to do that,” Okonedo says. “The way we filmed, it was quite chaotic and very raw. … So it wasn’t actually that difficult to kind of imagine yourself in that situation.”

Additionally, as the mother of a 7-year-old girl, Okonedo says she could relate to the feelings Tatiana must have had of wanting to protect her family at all costs. Having that basis to work from helped Okonedo get through several highly charged and emotional scenes that were largely improvised.

“I left myself completely open,” she says. “Obviously, you do quite a bit of research before you start to give yourself a social, emotional and physical context. Once the cameras start rolling, you can’t throw that away because you can intellectualize what happens in the scene. If you stay open then often the extraordinary might happen. If you study it too much it doesn’t happen.”