Released in 1980, "Superman II" is the sequel to the movie that kicked off the franchise starring Christopher Reeve as the Man of Steel. Also featuring Gene Hackman, Ned Beatty, Margot Kidder, Terrence Stamp and E.G. Marshall, the film was well received by critics and was the third-highest-grossing film of 1981.
General Zod, Ursa and Non
Before the explosion of Superman's home planet, Krypton, his father, Jor-El, imprisons three criminals in the Phantom Zone and sends them tumbling through space. Coincidentally, as the caged trio nears Earth, Superman happens to be disposing of a hydrogen bomb by flinging it into space; the bomb explodes and shatters the Phantom Zone, freeing General Zod, Ursa and Non. The intergalactic criminals first attack a group of astronauts on the moon and then descend to Earth to continue wreaking havoc.
No Longer Superman
Meanwhile, Lois Lane has begun to suspect that her colleague Clark Kent is really the man upon whom she has a crush, Superman himself. When Clark confirms her suspicions by accidentally plunging his hand into a fire and pulling it out unscathed, he is forced to admit his true identity to her. He whisks Lois off to his arctic hideaway, the Fortress of Solitude, where he decides to take the plunge and live his life with Lois as a regular man without super powers. Via a special process using a red crystal, his powers are removed, presumably forever.
Lex Luthor's Meddling
Unbeknownst to Superman, Lex Luthor has already found his way to the Fortress of Solitude and discovered both Superman's history and the story of Zod, Ursa and Non. Luthor vows to help the Kryptonian heroes in their quest to conquer Earth and Superman. He finds the trio after they've forced the President of the United States to surrender the planet to them, and Luthor explains that Superman is the son of the man who imprisoned them. He offers to deliver Superman to them, and in return Zod gives him dominion over Australia.
Superman Saves the Day
Upon learning of the super criminals and realizing he made a big mistake by giving up his powers, Clark makes his way back to the Fortress of Solitude and fortunately finds an antidote to the red crystal. Once again Superman, he returns to Metropolis and confronts Zod and his companions. Luring the trio back to the Fortress, Superman tricks them into exposing themselves to the red crystal, robbing them of their super powers. After that, defeating them is easy. A little super mind control on Lois to make her forget his secret identity, and everything is back to normal.