Ben Foster hopes his latest film The Program will make people put themselves in Lance Armstrong's shoes - and "have a conversation" about what they would do.
Foster stars as Armstrong in the biopic, which covers his rise to glory as a Tour de France champion, and his fall from grace after dogged sports journalist David Walsh (Chris O'Dowd) is determined to expose the truth: that the cyclist was a doping cheat.
Speaking at the gala premiere of the film in London's Leicester Square as part of the BFI London Film Festival, the actor said: "My hope is that people leave this film and have a conversation about what they would do themselves.
"If you had that much power and control, and you'd done that much good for people in the cancer world - half a billion dollars he raised - but he also took drugs, when everyone else was taking drugs as well. It's a complicated storyline. Have a conversation about it: what would you do?"
Armstrong admitted to doping in 2013, after years of strenuous denial.
The testicular cancer survivor was the most successful rider in the history of the Tour de France, winning seven times. He also founded the successful Livestrong Foundation, which provides support for people affected by cancer.
Foster, 34, has previously revealed in a Guardian interview that he took performance-enhancing drugs to prepare for the role.
Responding to media interest in that disclosure, he said: "I think it's representative of this story [Armstrong's]: what takes off and what people are attracted to is not necessarily the real whole, entire story. It's just part of it."
The film is based on real-life journalist David Walsh's book, Seven Deadly Sins: My Pursuit of Lance Armstrong. Walsh said seeing himself on screen played by O'Dowd felt like "an incredible thing that I never believed would happen. Flattering, too. I feel that Chris gets what it's like to be a journalist in the film. He looks like a journalist with a bee in his bonnet, and that's what I was for 12 years".
Director Stephen Frears said: "It's such an impressive crime. It's such a fantastic thing to have stolen the Tour seven times. I thought that was rather classy."
On Foster, he said: "He's terrific. If we hadn't got Ben we wouldn't have a film."
Producer Tracey Seaward said they hadn't engaged with Armstrong while making the movie. She said: "Sometimes when you're dealing with something quite controversial, you need to retain a level of impartiality in making the movie. It's very difficult if you're going to make a movie about someone as controversial as Lance if you're going to deal with someone's subjective story."
Co-producer Kate Solomon added: "What's really interesting about this story is that although it's about Lance, it's really about everyone. We all helped put him up there. Hopefully when people watch this, they come away thinking: what choices would I make? And would I have done the same thing?"
:: The Program will be released in cinemas on Friday, October 16