To illustrate Kyle’s divided nature, Eastwood fills in his backstory with compelling economy, flashing back to his Texas childhood. We see him out hunting with his father, dropping a deer with a difficult shot. We see the whole family in church, and later, at the family dinner table, we hear his father explaining his stern view of the world. There are three kinds of people, he says: sheep, who “don’t believe evil exists”; wolves, the evil men who prey upon them; and sheepdogs, men with “the gift of aggression,” a “rare breed that lives to confront the wolf.” Kyle knows which sort of man his father wants him to be.

Appalled by the 1998 Al Qaeda attacks on U.S. embassies in Nairobi and Dar es Salaam, Kyle enlists in the Navy and trains to join the SEALs, the service’s elite sea-air-and-land division. In a bar one night, talking to the woman who will soon become his wife, he tells her, “I’d lay down my life for my country. It’s the greatest country on earth.”

When Kyle deploys to Iraq for the first time, Eastwood shows us how he reconciles his deepest beliefs—his religious faith, his patriotism, his family values—with his duties as, essentially, a professional killer. He appears to have no interest in the political forces in which he’s caught up, and this enables him to tightly narrow his focus. He wants only to protect his fellow fighters and to dispatch the evil enemies who seek to annihilate them. Nothing else matters. But his determination to maintain this difficult mental balance begins eating him up inside.