But as much as Eastwood's American Sniper depicts life during wartime, it is equally about its aftermath, notably soldiers who return home to fight another battle with post-traumatic stress disorder (PTSD).
Tragically, for Kyle's family - his widow Taya and two young children - it's a condition with which they are all too familiar. Kyle and a friend were shot and killed at a Texas shooting range by a veteran Marine reportedly suffering from the condition.
As the rodeo competitor-turned-Navy Seal, Bradley Cooper is practically unrecognisable in the movie. Speaking with a heavy Texan drawl and an even heavier frame (he gained 18kg), Cooper disappears into Kyle's stoic alpha male.
The performance certainly bolsters Cooper's career trajectory, following his 2013 Academy Award nomination for Best Actor for Silver Linings Playbook (2012), and another last year as Best Supporting Actor for American Hustle (2013).
Bradley Cooper in The Hangover
Further proving his mettle as one of Hollywood's top leading men, Cooper, 40, is playing John Merrick - The Elephant Man - on Broadway to rave reviews.
In Manhattan to talk about American Sniper, Cooper explains this film is more personal than others, as he was one of the producers who approached Kyle to put his story on screen.
"I talked to Chris one time. We started negotiating with him in February of 2011. He had trepidation about the whole idea. I called him and said that I understood his fears about Hollywood, and that even though we don't know each other, I told him, 'I am going to do right by you and I want you to participate'.
"I told him I was going to spend time with him, but I was worried because I'm so different. I'm from Philadelphia, he's from Texas. I'm a buck-eighty-five [84kg], he's two-thirty."
Cooper resolved to do everything he could to play Kyle as convincingly as possible.
"So I became like a science experiment. I started with 6000 calories a day and went through extensive weight training.
"Chris was a massive, impressive Texan. I also had a dialect coach and I had to train with the sniper rifles.
"Then I met Chris' father." He pauses. "Clint and I went to Texas and spent time with his family, with his wife Taya and his children. It was very intense. If you can imagine, standing across from a guy whose son was murdered a year prior, saying, 'We are from Hollywood and we're going to make a movie about your son'. That's a crazy, very surreal thing; a huge responsibility."
He pauses for a moment, trying to remain composed.
I ask if there were any lighter moments during filming. "I had to remove my sunglasses [in one scene] but I was worried it would look like I was in a sunglasses commercial."
He does a crack impersonation of Eastwood's response to his concern: "You just put the glasses on and take them off."
A couple of hours later, Eastwood hears about Cooper's spot-on impersonation and breaks into a laugh. "Well, I haven't seen his imitation and it's probably best that I don't."
Clearly impressed with Cooper, he offers, "Bradley put his heart and soul in it. And the best compliment I can pay him is that I never caught him acting. So many times actors overact or get flashy, but he didn't. He had a real grasp on it." War is a familiar subject for Eastwood, who has also helmed Heartbreak Ridge, Flags of Our Fathers, and its companion film, Letters from Iwo Jima.
"War stories were popular when I was a kid and they remain that way. It's a very dramatic time; it's life and death and hardship. The basis of drama is conflict and wars are very conflicting so they are fun stories to tell as far as drama. But this film became more interesting because I went into the drama of the family."
Kyle's wife is played by Sienna Miller, until recently famed and almost always hired for her good looks rather than her acting chops. Miller, who also impressed critics with her turn in Foxcatcher, turns in a transformative performance as Kyle's widow Taya, a spirited Oregon brunette.
Sienna Miller plays wife Taya in American Sniper
"Of course I was raised in England and this is real America so it was completely foreign to me on many levels. For me, I don't understand guns, it's just not where I'm from," she says, yet plays the role with a believable intensity. "To get into the mindset I talked to a lot of military wives and spent a lot of time with Taya. We spoke extensively, which was invaluable. I had to bear in mind that she is a different woman now than the one I played in the movie who would go through this unspeakable tragedy."
The biggest tragedy of the story is that Kyle did not die in combat. In February 2013, he and a friend were shot dead on a shooting range in Texas by 25-year-old veteran Marine Eddie Ray Routh. Kyle had taken him to the range to help him over his PTSD. Routh is awaiting trial for Kyle's death.
"I'd never played a real person before," says Cooper. "I sat in the chair he used to sit in for dinner, and Sienna and I watched all the videos that Taya had taken of the family. There was a lot of footage because she never knew if he would return from the tours in Iraq. I'd be sitting there thinking to myself, 'Life is so surreal'. You'd see the date on the bottom of the video that read November. He was murdered three months later. The fact that I'd be watching the video knowing that was crazy."
Director Clint Eastwood
Arguably, Eastwood's American Sniper is a flag-waving salute to America. Like many soldiers, Kyle was a tunnel-visioned patriot whose duty to God and country almost seemed to precede his familial priorities.
"Chris was very torn about his country and family responsibilities. Personally, I would stay with family but when push comes to shove those are very hard choices to make."
Eastwood too considers the age-old theme about why men repeatedly return to put themselves in the line of fire since the beginning of time.
"I've been asking myself that since a very young age. Where does it end and does it ever end? That's for philosophers in centuries from now to figure out. Will mankind comes to its senses? Maybe not. You can get very fatalistic or cynical if you're not careful.
"I was 11 years old when World War II broke out, and I remember thinking that there won't be any more wars after that. But then in 1951 I was drafted into the army at the height of the Korean War. We all wondered what the hell we were doing there, and in later years, the same question was asked about Vietnam. After World War I, people said that that was the war to end all wars."
To his credit, Eastwood handles the material without over-sentimentalising it, though, regardless of political views and patriotism, there is no denying that Chris Kyle was a hero to his comrades.
Lowdown:
Who:
Bradley Cooper, Sienna Miller and Clint Eastwood
What:
American Sniper
When:
Opens today
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