Anti-Monitor

The Anti-Monitor is a fictional supervillain appearing in American comic books published by DC Comics. He was the main antagonist of the 1985 storyline Crisis on Infinite Earths and later appeared as a enemy of the Green Lantern Corps and Justice League.

Origins
During the Crisis on Infinite Earths, it was revealed how the existence of all parallel universes in the Multiverse came to be, including the positive matter multiverse and also the anti-matter universe, and how the Monitor and the Anti-Monitor came into existence; when the menace posed by the Anti-Monitor became apparent, several villains were sent back in time to stop him, but were defeated by Krona and the other Oans.