Ilya and Alexander Salkind, along with producing partner Pierre Spengler, purchased the film rights to the Superman property in August 1974. It was agreed that the Salkinds would produce and supervise filming on Superman and Superman II simultaneously, as had been the case with The Three Musketeers and The Four Musketeers.
As casting started to take place, and Alexander Salkind wanted a famous actor in the role of Superman. Dustin Hoffman was once again highly considered though the idea was dropped. Robert Redford was offered the part, but he felt he was too famous and was not right for the role, as did Burt Reynolds. After the success of Rocky, Sylvester Stallone lobbied hard for the role but was ignored. Paul Newman was offered all three roles of Superman, Jor-El and Lex Luthor to his choosing though he did not accept any of them, for a salary of $4 million. Nick Nolte and Rex Harrison would both turn it down. It was decided to focus on casting Jor-El and Lex Luthor and save Superman for later. Hoffman was then offered the role of Luthor, and although he was interested, he turned it down. Marlon Brando would eventually be cast as Jor-El, causing Gene Hackman to be cast as Luthor as he wanted desperately to work with Brando. Impressed by the producers' ability to cast famous actors in respective roles, Warner Bros. decided to distribute the film internationally, rather than simply domestically. The filmmakers made it a priority to shoot all of Brando's and Hackman's footage "because they would be committed to other films immediately."
During My Life, Stark Hesseltine told Christopher Reeve that he had been asked to audition for the leading role as Clark Kent/Superman in the big budget film Superman. Lynn Stalmaster, the casting director, put Reeve's picture and résumé on the top of the pile three separate times, only to have the producers throw it out each time. Through Stalmaster's persistent pleading, a meeting between director Richard Donner, producer Ilya Salkind, and Reeve was arranged. The morning after the meeting, Reeve was sent a 300-page script. He was thrilled that the script took the subject matter seriously, and that Richard Donner's motto was verisimilitude. Reeve flew to London for a screen test, and on the way was told that Marlon Brando was going to play Jor-El and Gene Hackman was going to play Lex Luthor.
When Hackman was initially cast, he was sporting a full head of hair and mustache unlike the Lex Luthor of the comics. Hackman was however, reluctant to shave his head or his mustache. So director Richard Donner made a deal with Hackman that if he shaved off his mustache, he would shave off his own. Hackman relented and when he returned to the set, Donner had revealed that he was sporting a fake mustache the whole time, which caused Hackman to laugh. Hackman did, however, get to keep his hair. In the film, Hackman's hairstyle was changed in every scene to create the illusion he was wearing wigs.