Nine days before the start of production, neither Quint nor Hooper had been cast. The role of Quint was originally offered to actors Lee Marvin and Sterling Hayden, both of whom passed. Zanuck and Brown had just finished working with Robert Shaw on The Sting, and suggested him to Spielberg. Shaw was reluctant to take the role since he did not like the book, but decided to accept at the urging of both his wife, actress Mary Ure, and his secretary.

The role of Brody was offered to Robert Duvall, but the actor was interested only in portraying Quint. Charlton Heston expressed a desire for the role, but Spielberg felt that Heston would bring a screen persona too grand for the part of a police chief of a modest community. Roy Scheider became interested in the project after overhearing Spielberg at a party talk with a screenwriter about having the shark jump up onto a boat. Spielberg was initially apprehensive about hiring Scheider, fearing he would portray a "tough guy", similar to his role in The French Connection.

For the role of Hooper, Spielberg initially wanted Jon Voight. Spielberg's friend George Lucas suggested Richard Dreyfuss, whom he had directed in American Graffiti. The actor initially passed, but changed his decision after he attended a pre-release screening of The Apprenticeship of Duddy Kravitz, which he had just completed.

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