Did you forget who I am? How I got to be the boss of bosses? I'm here, because I'm the baddest of the bad. Anybody who ever stood in my way is dead! Everybody!
~ Ultraman to Lex Luthor.
Ultraman is the name of several DC villains, all of whom are evil versions of Superman - the current holder of the title is said to be the Superman alternative from the antimatter-universe, as a resident of the antimatter universe, he is a devoted worshiper of evil and thus in direct opposition to the ideals, his mainstream counterpart stands for.
Ultraman is not to be confused with the clone of Superman that went berserk in Superman: Doomsday, though the two are similar concepts Ultraman is defined as the dark-half of Superman made flesh rather than a simple clone-turned-bad - being born in another universe and thus possessing similar powers to the mainstream Superman but used purely for selfish and/or immoral gain.
Ultraman has not been seen very often in publishing outside the comics, though other villainous versions of Superman have - such as the rogue Superman from Justice Lords - however Ultraman himself appeared in the 2010 animated film Justice League: Crisis On Two Earths and also appeared in the DC Universe Online videogame.
Ultraman, along with the other leaders of the Crime Syndicate, appear as the secondary antagonist in the animated movie; Justice League: Crisis on Two Earths. He was voiced by Brian Bloom, who voiced him with a stereotypical Mafioso accent.
Though Ultraman doesn't appear in the TV show; Smallville, there is an alternate version of Clark Kent known as Clark Luthor, to which fans have considered him as Ultraman. This version was of Clark was adopted by the Luthor Family instead of the Kents. He was also taught to never hold back with his powers. As a result, Clark Luthor could use other powers that Clark Kent can't use, became Earth 2's most dangerous supervillain, and even killed his adopted brother Lex Luthor.
Ultraman in Justice League: Crisis on Two Earths
Ultraman's origin (a twisted parallel to Superman's own)