During six years of service in Iraq, Kyle notched up some 160 confirmed kills, becoming such a threat to Iraq's insurgents that they put their own US$80,000 (NZ$103,029.99) bounty on his head.
The biopic is directed by Clint Eastwood and stars Bradley Cooper as Kyle. It has been nominated for six Oscars and compared with Hollywood's other big Iraq war nail-biter - Kathryn Bigelow's The Hurt Locker, which chronicled the life of bomb-disposal experts in Baghdad.
But that is where the similarities end.
First, American Sniper shifts the action an hour's drive west to the cities of Fallujah and Ramadi, the self-declared "graveyards of the Americans" that make Baghdad look almost benign. And second, in concentrating on the role of the sniper, the film zeroes in on an altogether darker, psychologically murkier side of warfare.
For while bomb-disposal men save lives single-handedly, snipers take them single-handedly, and often in very great numbers. Most soldiers can fight entire wars without getting anywhere near the tally that Kyle amassed, for the simple reason that gun battles are usually far too chaotic to be certain as to who shot whom. A sniper, by contrast, plays "God" over those who come in his sights, decreeing who lives and who dies, and watching the instant results in close-up telescopic vision.
So what kind of person becomes a sniper? If Kyle's example is anything to go by, people who are not too plagued by inner doubts about what they do. The US military does rigid psychological screening of any soldier wanting to specialise as a sniper, but even so, it is hard to imagine them finding any better candidate than Kyle, whose God 'n' guns backstory - recounted in a 2012 autobiography that became a New York Times bestseller - sounds like something out of a US military recruitment advert.
Born in Texas to a deacon and a Sunday school teacher, Kyle got his first rifle at the age of 8, starting out by shooting quail and deer. Before the army, he worked as a rancher and professional bronco rodeo rider, chewing tobacco, sipping whisky, and never walking away from a barfight. He lists his priorities as "God, country and family" in that order. And in his autobiography, he makes it very clear that those who tried to kill his comrades richly deserved the fate he dished out in spades.
"People ask me, 'How many people have you killed?'" he writes. "The number is not important to me. I only wish I had killed more. Not for bragging rights, but because I believe the world is a better place without savages out there taking American lives."
On the final page, he adds: "When God confronts me with my sins, I do not believe any of the kills I had during the war will be among them."
For Kyle, the sheer brutality of many of his enemies, who killed far more fellow Iraqis than they did Americans, eliminated any doubts: in the film, one of his targets is a torturer called the Butcher, who more than lives up to his nickname. Besides, were the Almighty to decide he did want to scrutinise Kyle's formidable kill list, it would take a very long time to go through them all. His tally of 160 was a conservative estimate based on kills corroborated by other soldiers. The real figure, he reckoned, was more than 250, if one counted "the ones that got away" - those who crawled out of sight before dying.
Even so, Kyle did not claim to be a particularly outstanding shot. He simply claimed that Iraq gave him a lot of chances. On one occasion, he shot seven dead in a single engagement. On another, he killed two insurgents on a motorbike with a single bullet.
More to the point, Kyle's skills also won the ultimate accolade from his enemies, who nicknamed him the Shaitan Al-Ramadi (The Devil of Ramadi). After leaving the military in 2009, the man who was still a faceless killer to his enemies became a minor celebrity in the US, featuring on the cover of Soldier of Fortune magazine and appearing on chat shows. That he could even show himself on television is proof of how America still loves guns and those who excel with them, especially in service of their country. In Kyle's case, though, the biggest feeder of the legend was himself. As well as setting up his own successful military training company, he also featured in Stars Earn Stripes, a reality TV show in which ex-soldiers helped celebrities like Todd Palin - husband of ex-Alaska governor Sarah - brush up their military skills. On one occasion, he was said to have shot and killed two Mexican bandits who tried to carjack him outside a petrol station. On another, he claimed to have holed up in New Orleans post-Hurricane Katrina and shot looters from the top of the Superdome. The US media could find nothing to prove that they were anything other than bar-room boasts.
Like many other veterans, he sustained a degree of combat trauma and this made it hard to get used to life back in Texas.
Ironically, it was his own efforts to readjust that lead to his ultimate undoing. Having recognised his own post-combat difficulties, Kyle used his celebrity status to help start the "Heroes Project" to provide fitness training and life-coaching to disabled and traumatised veterans. Among those he helped was a troubled young ex-Marine called Eddie Ray Routh, whom Kyle invited to a rifle range at Rough Creek Lodge, Texas, in 2013.
For Routh, it should have been the perfect therapy. Instead, Kyle became the target. For reasons that are unclear to this day, Routh shot Kyle dead, and also one of Kyle's friends, Chad Littlefield. He was later arrested while driving Kyle's pickup truck.
Film divides Hollywood, audiences
The Oscar-winning documentary maker Michael Moore has criticised the US Army's use of snipers at the same time as a film about it has broken box office records, and seen a flurry of racist reaction on Twitter.
American Sniper has broken US box office records as the biggest drama and January opening of all-time, with US$90.2 million ($116 million) tickets sold on its first weekend.
Moore criticised the concept of snipers, and the US army's presence in the Middle East, on Twitter. "My uncle killed by sniper in WW2. We were taught snipers were cowards. Will shoot u in the back. Snipers aren't heroes. And invaders r worse" he tweeted. "But if you're on the roof of your home defending it from invaders who've come 7K miles, you are not a sniper, u are brave, u are a neighbour."
Actor Rob Lowe responded to Moore on Twitter by tweeting: "He's kidding, right?"
Seth Rogen compared American Sniper to a Nazi propaganda film in Quentin Tarantino's Inglourious Basterds.
The film has also triggered a racist outpouring from audiences on Twitter and a countersurge from people who found the film to be racist.
Negative reaction includes:
@dancohen3000
I watched American Sniper. It's a racist whitewash of history that canonizes a mass murderer.
@bugbae
please please please do not go see american sniper it's propaganda to further promote and normalize islamophobia
A collection of racist reactions to the film originally posted by @leslieK-nope has been been recirculated thousands of time on different accounts.
