
Superman has confirmed Ultraman's true identity, which differs slightly from the character's typical portrayal in DC comics. Ultraman has been teased as a black mask-wearing antagonist in several of Superman's trailers, appearing as one of Lex Luthor's allies who intends to take down David Corenswet's Man of Steel. The anti-Superman is a well-known figure in DC comics, but James Gunn's new superhero film has an intriguing way of utilizing Ultraman.
Theories have been circulating for months regarding Ultraman's true face, which has been consistently hidden behind a black face mask and goggles in marketing materials. Some theories suggested Ultraman could be hiding the face of another DC hero, while others suspected the masked character may be harboring multiple secret identities and is also behind the helmet of the mysterious Hammer of Boravia. Now that Superman has been released, the whole story of Ultraman has been revealed.

Warning - The rest of this article contains spoilers for Superman.
Ultraman is introduced secretly in the very opening scenes of Superman, where he is revealed (as was speculated) to be the man behind the mask of the armored Hammer of Boravia. The character is shown to be intricately controlled by the technicians at LuthorCorp, with Lex Luthor (Nicholas Hoult) himself calling the shots for the specific attack moves that Ultraman should use in the fight against Superman.
After ditching the Hammer of Boravia moniker, Ultraman is seen several times again throughout Superman, depicted as a super-strong but silent figure who is blindly loyal to Luthor's every command. He assists with breaking into the Fortress of Solitude and also fights Superman alongside the Engineer in Metropolis' stadium.

Towards the end of the film, Ultraman's true identity is revealed when his mask is removed to reveal the face of Superman himself (also played by Corenswet).
Ultraman's True Face in Superman Explained

It's not surprising that the face beneath Ultraman's disguise mirrors Superman's. The character is often depicted as a dark mirror image of Superman in DC Comics, and the same can be said here. However, the explanation for Ultraman's origins in Superman differs from his comic backstory.
During Superman and Ultraman's fight sequence in the final act, Luthor explains to Superman that Ultraman is his clone, which the villain was able to fabricate after combing the remains of Superman's battlegrounds for a piece of hair. While Ultraman has all the same abilities as the Kryptonian, he has none of the smarts or personality, and Lex describes Ultraman as being significantly "dumber" than Superman. This explains why Lex has programmed Ultraman to follow his every move, as he does not trust the clone to be smart enough to win the fight on his own
In DC Comics, Ultraman is typically a version of Superman from another universe who leads a Multiversal crime syndicate. However, in this iteration, Ultraman's backstory as a clone of Superman lends itself to a different DC comics character: Bizarro.
In the comics, Bizarro is a clone of Superman who was commissioned by Lex Luthor to replicate the Man of Steel. His version resulted in a flawed mirror image, with his distinguishing feature being his gray skin. In some iterations of the character, Bizarro is also depicted as mute and with limited intelligence, similar to how he is in Superman.

Rather than sticking closely to either of these comic origin stories, Gunn's Superman combines the characters of Ultraman and Bizarro, utilizing pieces of both characters' personalities and backstories. While the character goes by the name of Ultraman and has the same face and abilities, his origins and personality are closer to Bizarro's.
Superman ends up defeating Ultraman in the movie by throwing him into the black hole that has opened within Metropolis, leaving the villain to float through the ether of space. This could open the door for Ultraman to return one day, perhaps leaning further into his identity as Bizarro. Or it could be that Ultraman was a one-and-done and that Gunn will draw on the gallery of other prominent Superman villains for his next primary foe.