Superman has fought plenty of powerful villains, but his darkest foe is actually a reflection of himself. Originally known as Superboy-Prime, this maniacal Man of Steel from an alternate universe would later change his name to Superman-Prime, but the reasons for the switch are more complicated than fans might think.
Superboy-Prime hails from another world called Earth Prime, where DC heroes exist only in comic books. However, things change in DC Comics Presents #87 when Superman from Earth-One crosses over into Earth-Prime. A passing comet causes Superboy-Prime’s powers to kick in, after which the two team up to stop a tidal wave. Being his world’s only superhero, Superboy-Prime develops a bit of a god complex, which spirals into madness following the events of Crisis on Infinite Earths that destroy his whole reality. However, it was Infinite Crisis by Geoff Johns that made Superboy-Prime a full-fledged villain as he breaks free from the paradise dimension to wage war on the heroes of Earth-One. The DC heroes eventually defeat Superboy-Prime, turning him over to Green Lantern's Guardians of the Universe for imprisonment, but by the next time he appeared, he was a boy no longer.
In an interview with Newsarama, writer Geoff Johns spoke on 2007’s Sinestro Corps War event, in which Superboy-Prime had a big part to play. When the Anti-Monitor’s forces attack Oa, they recruit the displaced Kryptonian to their ranks, but this time around, he insists on being called Superman-Prime. Johns revealed that this was, in part, due to legal issues. Superboy's character had been steeped in legal trouble since his conception. Superman co-creator Jerry Siegel had actually pitched Superboy to DC in 1938 but was rejected. However, the company later decided to move forward with the idea without him, sparking a lawsuit.
The court ruled that Superboy should be treated as a separate, non-derivative of Superman from a legal perspective, but both parties eventually agreed to make the character DC’s property. However, copyright laws would continue to evolve over the decades, giving creators more chances to seek ownership of individual characters. Eventually, Siegel’s heirs attempted to reclaim the rights to Superboy in the early 2000s. Several years of lawsuits and court cases followed, and with ownership of the character in flux, comics being written at the time had to avoid using the Superboy name, hence the change to Superman-Prime.
While some progress has been made over the years, copyright laws around comic book characters can still be difficult to dissect. Disputes between Sony and Marvel Studios nearly led to Spider-Man leaving the MCU, and in the same vein, the rights to a standalone Hulk movie are tied up with Universal Studios, meaning another MCU Hulk solo film may never happen. However, as far as Superboy-Prime goes, the name switch to Superman-Prime actually made sense within the story. The character had aged an extra several years after being trapped in the Speed Force and several more as a prisoner on Oa, but even beyond that, Superboy-Prime had been hardened by his experiences. Not only was he the sole survivor of his Krypton; he was the sole survivor of his entire reality. Being called “boy” implies some level of innocence, so with all he had seen and done, it made sense for the character to go by Superman-Prime instead.
Eventually, the rights to Superboy returned to DC, causing the character’s name to switch back to Superboy-Prime in subsequent appearances. Even still, the case of Superman-Prime goes to show that the impact of copyright laws on a comic’s story can sometimes work out in unexpected ways.
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