A remake of Akira Kurosawa's Yojimbo (1961), and also a variation on Dashiell Hammet's novel Red Harvest (1929), this is the one in which Eastwood plays two warring cowboy factions against one another, and also the one in which he gets beaten to a bloody pulp.
It's no secret that A Fistful of Dollars is a straight-up copy of Kurosawa's 1961 samurai picture Yojimbo , one that didn't even have the decency to credit the original film - "no secret", hell, it's maybe even the single most famous fact about Leone's film.
He directed Rashomon and Ran, and his Seven Samurai was remade in to The Magnificent Seven, his Yojimbo was remade as A Fistful of Dollars and Last Man Standing.
Though distinctly of a piece with the samurai/ronin narrative tradition, Yojimbo largely takes its cues from the archetypal American western, and in turn inspired two Western remakes, Sergio Leone's A Fistful of Dollars and Walter Hill's Last Man Standing.
Borrowing heavily from John Ford's westerns, Kurosawa in turn inspires the famous "American" clone that established the "spaghetti western" genre and firmly planted Clint Eastwood as an icon—Sergio Leone's A Fistful of Dollars.
One of the most popular of all Kurosawa's movies, Yojimbo has also provided the template for Sergio Leone's A Fistful of Dollars and Walter Hills's Last Man Standing.