Although the film received mixed reviews, John Sturges got a rave from the one source that really mattered to him. Akira Kurosawa was so impressed he sent the American director a ceremonial sword as a gift.
Yul Brynner had a major say in casting decisions. He specifically requested that Steve McQueen be cast as Vin Tanner. Brynner later regretted the move because he and McQueen became enemies on set.
The "bandit gang" hired for Calvera adopted Eli Wallach as one of their own. In the mornings before shooting started, but after Wallach was in costume, he and the group would go riding together for an hour. Additionally, members of the gang insisted on doing the final checks for Wallach's horse tack and prop gun before he was allowed to use either.
The oneupmanship between Yul Brynner and Steve McQueen spread to the other actors, and they all started pulling stunts of their own in order to get the audience's attention. While a lot of the attention-hogging did make it into the finished film, John Sturges was terrified by how quickly he lost control of his cast.
James Coburn was a big fan of Seven Samurai (1954) and his favorite role in that film was the character that he ended up playing in the Americanized version. He deliberately incorporated Seiji Miyaguchi's performance as Kyuzo into his performance.