When Warren Beatty was on-board as producer only, his sister Shirley MacLaine was a strong possibility to play Bonnie. But when Beatty decided to play Clyde himself, for obvious reasons he decided not to use MacLaine.
Warner Bros. had so little faith in the film that they offered first-time producer Warren Beatty 40% of the gross instead of a minimal fee. The movie went on to gross over $70 million.
In real life, Clyde Barrow was a highly dangerous marksman who had mastered most firearms, including the Browning automatic rifle and the Thompson submachine gun. The lawmen chasing him were well aware of his ability with a gun, which partly explains the ruthlessness behind the way he was gunned down.
Gene Hackman was on the set one day when he noticed a guy standing behind him and staring. The man said, "Hell, Buck would've never wore a hat like that." Hackman turned around and looked at him and said, "Maybe not." He looked like an old Texas farmer. The man introduced himself and said, "Nice to meet you. I'm one of the Barrows."