This legendary moment in cinema blew everyone away, including the cast of the film itself. The big reveal that Darth Vader was Luke's father was kept secret from almost the entire cast until the final film was released. The filmmakers accomplished this by having Vader's actor, David Prowse, say that Obi-Wan killed Luke's father instead, with James Earl Jones dubbing the real dialogue later in production. Only Irvin Kershner, George Lucas, and Mark Hamill knew the dialogue would be voiced over later, and they kept the secret until the film was released.