What makes a hero? A righteous person doing righteous things to help others in a righteous cause? Sure, that's easy enough. But must the things he does be righteous? What if the cause is not? Those are trickier questions that come to mind right at the beginning of "American Sniper," Clint Eastwood's film about Navy SEAL Chris Kyle, portrayed with intensity by Bradley Cooper. Not that Eastwood has any trouble answering them. His belief in a simple good vs. evil scenario is unwavering, which may be troublesome to some. But to Kyle, on whose autobiography the film is based, the question doesn't even exist. Good guys kill bad guys, period. It is to Cooper's credit — and Eastwood's — that Kyle does not come off as a lunk-headed cartoon hero, but a man who, if he doesn't struggle with his choices in the moment, is gravely affected by their consequences. As for the good guys killing bad guys, Kyle killed more than anyone armed with a rifle. He is recognized as the U.S. military's most-lethal sniper, with 160 confirmed kills and scores of others likely in four tours in Iraq. It is a staggering number that earns him the nickname "Legend" among his appreciative colleagues. (He provides them cover on their missions.) But it also exacts a toll. At the beginning of the film, Kyle is a Texas rodeo cowboy, his life no more settled than the back of a bucking horse. Military service gives him purpose, and he learns quickly that he is not just an exceptional marksman but a man willing to take the difficult shot (in more ways than one) that may force others to hesitate. What he — and, under Eastwood's direction, the audience — sees through the scope on his rifle is not always a bad guy in a black hat. This is an enemy that employs women and children in its campaign. How do you fight against that? And what becomes of you when you do? Bradley Cooper (right, with Kyle Gallner) plays Chris Bradley Cooper (right, with Kyle Gallner) plays Chris Kyle, the most prolific sniper in U.S. history. (Photo: Warner Bros. Pictures) Kyle is steadfast in his sense of duty. His flirtation with and marriage to Taya (Sienna Miller) is buoyant, full of hope and dreams. But after he begins his service, his time at home lacks the purpose and single-minded focus of his job as a sniper — the lens widens to more than a target, and Kyle increasingly has trouble dealing with it. So he heads back to war. A subplot about Kyle's opposite number, a Syrian sniper who reportedly medaled in the Olympics, does not have the emotional payoff you might expect, and at times there is a sameness to the action. But it's never less than compelling; Eastwood's spare style pays off with a clarity and sureness. Some of Kyle's fellow soldiers begin to doubt the cause; the film suggests that such indecisiveness and moral ambiguity can be deadly. And perhaps for those with guns in their hands and targets on their backs, it can. For the rest of us, it's a stickier situation, fought in classrooms and editorial pages, not battlefields (which are often crowded streets and apartment buildings). For Kyle, it's a sacred duty, and one that he begins to sacrifice all else to. Miller is good as Kyle's suffering wife. If that implies she simply sits around crying, it shouldn't. She's tough, and although she believes in Kyle's cause, she wants her husband back. Her support and insistence on getting help are what bring Kyle back into his life away from the war. Related: Eastwood's 10 best films But it's Cooper's movie, and, although he has been good in pretty much everything we've seen him in, there is a depth to this performance we haven't seen before. It's a tricky balance: As the legend grows, the man diminishes. Cooper and Eastwood do an exceptionally good job of maintaining that. There is a cruelty to how the story plays out, in life and on film, but I won't reveal that in case you're unaware of it. Suffice it to say that some are able to leave the battle behind. Others are not. But Eastwood is adamant in arguing that the battle is worthwhile, nevertheless, for heroes.