Fistful of Dollars is a really good picture. Exciting, violent, funny, cynical, and not too long, it’s an excellent cowboy-south-of-the-border adventure, in the Vera Cruz vein. It’s heavily influenced by Yojimbo: the characters, the plot, and most of the incidents are lifted from Kurosawa’s film. Copyright doesn’t seem to have been an issue in the Italian cinema of the 1960s—films were continually borrowing plots and character names from other films—so Leone’s producers made no effort to contact Yojimbo's producers, or to obtain the remake rights. For them, the film's inspiration was something to be ignored…
By 16 December, Fistful of Dollars had taken 430 million lire at the box office. It was the most successful Italian-made Western, and one of the most successful Westerns generally… Given the Variety review and the film’s enormous box-office receipts, a letter from Mr. Kurosawa was inevitable. According to Tonino Valerii, Leone’s assistant, it arrived signed by Kurosawa and Ryuzo Kikushima, his co-screenwriter on Yojimbo. Valerii reported its contents to Frayling:
Signor Leone—I have just had the chance to see your film. It is a very fine film, but it is my film. As Japan is a signatory to the Berne Convention on international copyright, you must pay me. — Akira Kurosawa.
Leone was thrilled to receive a letter from a Master, congratulating him on his very fine film. But [producers] Papi and Colombo were appalled, and tried to mount a defense rather than settle. Perhaps inevitably, Leone became a part of it—though they were defending the indefensible. At the start, Leone had sent all his friends and collaborators to see Yojimbo. He had asked Colombo and Papi to obtain the rights. Now he and they began claiming that Yojimbo was only one of various sources which had inspired Fistful of Dollars… When the litigation delayed international sales, Papi and Colombo settled, giving Kurosawa and Kikushima Asian rights to Fistful, plus 15 percent of the international box office.