Henry Fonda, against type, plays Frank the main antagonist. He is a ruthless, selfish, and sadistic mercenary who was hired by the railroad tycoon Morton to manipulate people like McBain into moving off their land, but instead, he kills him and his family, and has only one other goal; kill Harmonica and Cheyenne.
Sergio had originally wanted Fond for the Man with No Name role in “Fistful of Dollars” but he could not afford him with his miniscule budget. Fonda did not accept Leone's first offer to play Frank, so Leone flew to New York to convince him, telling him: "Picture this: the camera shows a gunman from the waist down pulling his gun and shooting a running child. The camera tilts up to the gunman's face and...it's Henry Fonda." After meeting with Leone, Fonda called his friend Eli Wallach, who had co-starred in “The Good, the Bad and the Ugly”. Wallach advised Fonda to do the film, telling him "You will have the time of your life."
When he accepted the role, Fonda came to the set with brown contacts and facial hair including a moustache. Fonda felt having dark eyes and facial hair would blend well with his character's evil persona and also help the audience to accept this "new" Fonda as the bad guy, but Leone immediately told him to remove the contacts and facial hair. Leone felt that Fonda's blue eyes best reflected the cold, icy nature of the killer. It was one of the first times in a Western film where the villain would be played by the lead actor. Leone wanted the shock value of the audience seeing a ranch family massacred and they the villains move out of the dust and sagebrush to face the only survivor young Timmy McBain. When the camera panned around to show the face of the gangs leader he wanted the audience to gasp and say, “Jesus Christ, it’s Henry Fonda!”
Fonda discussing his role as Frank: https://www.youtube.com/watch?v=cHI6Hl7FUqA