Some of Gene Hackman's scene were actually filmed with a body double. That's because Gene Hackman quit before all of his scenes were shot.

Richard Donner, the director of Superman, was originally hired to make Superman II. He had made over half of the movie before being fired. Richard Lester was hired to complete the film. So, Superman II contains footage from both the Richard Donner version and the Richard Lester version.

Jack O'Halloran who played Non was a professional boxer between 1966 and 1974. He got as high a ranking as 5th in the world.

Marlon Brando was offered the opportunity to reprise his role as Jor-El from the first film, but he was unwilling to reprise his role for this film. As a result, we only see his hand at the beginning of Superman II, and we see only Superman's mom in the recap footage from Superman. Later in the movie, we only see Superman's mom in the crystal recordings for the same reason.