Wikipedia
Superboy-Prime, (Clark Kent, born Kal-El) also known as Superman-Prime or simply Prime, is a DC Comics superhero turned supervillain, and one of several alternate Supermen. The character first appeared in DC Comics Presents #87 (November 1985), and was created by Elliot S! Maggin and Curt Swan (based upon the original Superboy character by Jerry Siegel and Joe Shuster).
Superboy-Prime is from a parallel Earth called Earth-Prime that had no super-heroes. There, Superman and the other comic superheroes were fictional characters only seen in comic books. The Earth-Prime universe was erased during the Crisis on Infinite Earths, and Superboy-Prime ended up in a "paradise" dimension where during that time, he found himself unable to let go of his former life and his destiny as Earth's greatest hero.
Over time, his convictions and morals become twisted and warped, and he came to believe that Earth-Prime is the only proper Earth and that he, Superboy-Prime, was the only one worthy of the mantle of Superboy. Prime firmly believes that becoming Superman is his calling despite the fact that he has become a psychotic and murderous villain. His overwhelming strength, speed, and ruthlessness make him one of the most dangerous foes in the DC Universe.
The name "Superman-Prime" was first used by Grant Morrison in DC One Million (1998) for the mainstream Superman in the 853rd century. Earth-Prime's Superboy first refers to himself as "Superboy-Prime" in Infinite Crisis #2 (January 2006).