It is the fifth film in the Superman film series and a sequel to Superman III (1983). It is the first film in the series to not have the involvement of producers Alexander and Ilya Salkind. The film also marks the final appearance of Reeve as Superman, who agreed to return in exchange for a large salary and a story promoting nuclear disarmament.

Young Lenny Luthor breaks his uncle Lex Luthor out of prison. Returning to Metropolis, Lex and Lenny steal a strand of Superman's hair from a museum and create a genetic matrix. Lex converses with black-market arms dealers, disgruntled about Superman's actions, wanting to re-arm the countries with nuclear warheads, and makes a deal with them to attach the hair to a nuclear missile. After the missile is test-launched, Superman intercepts it and throws it into the Sun. A glowing ball of energy is discharged, which develops into a superhuman. This "Nuclear Man" makes his way back to Earth to find his "father", Lex, who establishes that while his creation is powerful, he will deactivate without exposure to sunlight. A vicious battle ensues between Lex's creation and Superman. While saving the Statue of Liberty from falling onto the streets of New York, Superman is infected with radiation sickness by a scratch from Nuclear Man's radioactive claws. Nuclear Man kicks Superman into the distance with such strength that Superman's cape falls off.

According to writer Mark Rosenthal's commentary on the 2006 DVD, in the gallery of deleted scenes included on the disc, there are approximately forty-five minutes of the film that have not been seen by the general public. They were deleted following a failed Southern California test screening. In fact, the Nuclear Man that appears in the film is actually the second Nuclear Man that Luthor created. Cut scenes featured the original Nuclear Man (portrayed by Clive Mantle) engaging Superman in battle outside the Metro Club and being destroyed by the Man of Steel. The first Nuclear Man was somewhat more inhuman-looking than his successor, and vaguely resembled in looks, and significantly in personality, the comic book character Bizarro. Luthor postulates that this Nuclear Man was not strong enough, and hatches the plan to create the second Nuclear Man within the sun as a result.

In February 2021, Ta-Nehisi Coates was revealed to be writing a new Superman film for the DCEU that was in early development. J. J. Abrams was set as producer alongside Hannah Minghella, with no director or actors attached to the project yet. The film was expected to feature a black actor portraying Superman, with potential for Michael B. Jordan to take on the role. Coates said he was looking forward to "meaningfully adding to the legacy of America's most iconic mythic hero", while Abrams said the film would tell a "new, powerful and moving Superman story". This was reported by outlets as being a reboot of the franchise, but Richard Newby of The Hollywood Reporter felt the film starring a black actor could indicate a new version of Superman that could exist alongside Cavill's portrayal within the DC Multiverse. Newby also noted that Coates' history as a non-fiction author and journalist focusing on African-American issues would give him "the insight and experience to delve further into the [Superman] mythos in a way never seen on screen".

The studio was in the early process of finding a director for the film at that point, and had committed to hiring a black filmmaker for the project. They had met with potential directors by early May, working from a list that included Steven Caple Jr., Ryan Coogler, J. D. Dillard, Regina King, and Shaka King. Coates was not expected to deliver his script for the film until mid-December, and was believed to be introducing a new version of Kal-El / Superman in what was potentially a 20th century period piece. The film was expected to be set in a separate universe from the DCEU at that point.