Superman: King of the World is a comic book one-shot, which finishes off the Dominus storyline in the early 2000s.
After Superman battles Dominus, he seemingly emerges victorious. However, he claims that Dominus has gotten away, and requests the cooperation of all world nations to help track him down. Soon, he is patrolling the world with the help of other superheroes and Superman Robots, and little by little starts taking over the world.
His friends start to grow suspicious of him, to the point where Lois Lane teams up with Lex Luthor to infiltrate his new tower to find out what's going on. They discover that Superman isn't really Superman at all, but Dominus, who has locked up the real man of steel and switched their appearances somehow.
They manage to release Superman, who then fights Dominus in the psychic arena. Using Kryptonian mental disciplines, Superman is able to triumph, sending Dominus into the Phantom Zone within a fantasy.