Yet this isn't your traditional Western shoot-'em-up.
"If it was just cowboys, it would be a pretty darn good cowboy story," says producer Steven Spielberg. "If it was just aliens, it would be a pretty good alien story unto itself, but then when you combine the two ... it's wonderful."
Director Jon Favreau, who is also behind the Iron Man movies, says: "My idea was to embrace both genres, and through the juxtaposition of the classic form of both the alien-invasion movie and the Western create something new and exciting."
Set in New Mexico in 1875, a stranger (Daniel Craig) awakens in the middle of a desert with no memory of his past. He finds a strange metal shackle attached to one of his wrists. He stumbles onto the frontier town of Absolution, which is ruled by iron-fisted mayor Colonel Dolarhyde (Harrison Ford). The stranger is recognised as the outlaw Jake Lonergan. A fight ensues and he is subdued by a mysterious woman named Ella Swenson (Olivia Wilde).
Soon, aliens appear from the sky and begin to attack Absolution, forcing old enemies to band together with Lonergan. His powerful alien shackle helps him fight the alien invaders.
"In the Western, everybody recognises the man with no name," producer Alex Kurtzman says. "He walks into town and everyone wonders who he is and what he's trying to do. The sci-fi spin on that is that he's the man with no name because he was abducted by aliens and forgot who he was."
Ultimately, it is the strange and novel clash of genres that will draw audiences. "In a world where studios are frequently looking for big titles, there aren't many that stand out - and this one did that for us," Kurtzman says.
Cowboys & Aliens opens on August25