Originally directed by Steven Spielberg, but he withdrew due to schedule reasons.
Bradley Cooper bought the copyright to the story, initially only intending to be a producer, starring Chris Pratt. But then, he changed his mind.
Cooper gains 40 pounds for the character, eats 8,000 calories a day, and runs for four hours a day for several months. He also watched a lot of video data of Chris Kyle during his lifetime.
Chris Kyle had an intersection with Marcus Luttrell, the "lone survivor" in reality. The two became close friends during SEAL training and have kept in touch since then. Marcus Luttrell's life was also put on the screen before, and the movie's name was "Lonely Survivor".
Chris Kyle's father had warned Eastwood and Cooper that if their movie hurt his son's reputation, he would never let it go. But he also said that he trusted the two of them.
David O. Russell, who has worked with Cooper on films such as "The Happiness Behind the Clouds", and another hallmark director Steven Spielberg have both considered directing this film.
Jamie Alexander, Kate Mara, and Evangeline Lily were all considered candidates to play Taya Kyle. The latter two abandoned the film for "Fantastic Four" and "Ant-Man" respectively.
Before Chris Kyle died, Cooper had a 2-minute conversation with him. To commemorate him, Cooper devoted 8 months to preparing for the movie role, dedicated to Chris and his family.
Eastwood made a brief cameo in the film. He walked into a church as a passerby, and Chris stole his Bible.
