The Mamma Mia! star takes on twice the work in the film, starring as Latif Yahia, an Iraqi man who was forced to work as a body double for Hussein's eldest son Uday, also portrayed by Cooper.
The Brit felt compelled to tackle the "incredible" script - and reveals several stars and moviemakers had refused to take on the project.
He tells FOX411's Pop Tarts column, "The story itself is incredible, I think a lot of actors and directors were tentatively scared of it when the script was first developed a few years ago, I know a lot of people decided not to take it on but I didn't fear that... I tried not to think about that too much, even now.
"It was real, this really happened to a man (Yahia) and he was emotionally and physically scarred from that."