The Anti-Monitor is a cosmic entity created and driven by a negative, meta-universal energy known as "Anti-Matter".
Residing within the Anti-Matter Universe; one of an infinite number of alternate universes within the Multiverse, the Anti-Monitor seeks to destroy and consume all other "positive-matter" universes to increase his own power and render his own "Anti-Matter" universe as the only reality in existence.
Maltusian scientist Krona performed a forbidden experiment in an effort to see the origin of the universe, however, his actions, though successful, disrupted the process of cosmic creation and resulted in the creation of a "Multiverse" and an additional, opposite "Anti-Matter" universe.
In this universe, the Anti-Monitor was born on one of the moons as an excess of great energy taking form. At that same time in the positive matter universe, The Monitor was born of similar origin.
Soon the Anti-Monitor took over Qward by force and created a legion of troops with the power to throw lightning bolts. These warriors became known as the "Thunderers of Qward". Members of the Thunderers that proved to be his most trusted and powerful were then altered into living Shadows. Once he sensed The Monitor in the positive universe, he began a 1,000,000,000 year long war with him, which ended in both of them losing consciousness.
After 9,000,000,000 years of inactivity from either Monitor, the gifted scientist Kell Mossa sought to learn the secrets of the origin of the universe much like Krona had done. Despite the council of his universe objecting, he created an Anti-matter chamber with which he safely observed the origin of the universe. While observing this, however, the Anti-Monitor and The Monitor were awoken and the Anti-Monitor destroyed Kell's universe.
After destroying Kell's universe, the Anti-Monitor drained its energy and found that not only had he become stronger from consuming the energy, the destruction of a positive matter universe caused the anti-matter universe to expand; also making him stronger. With this knowledge in hand, the Anti-Monitor set out to destroy all of the positive matter universes and, therefore, make himself the most powerful being in existence.
Once The Monitor realized what the Anti-Monitor’s plan was, he set out to prevent it and endowed Kell, now named "Pariah", with immortality and the ability to transport to other universes to act as a messenger to warn them of the on-coming threat, albeit ineffectually. In addition to this, The Monitor set up a series of towers that would protect Earth-One and Earth-Two from destruction, as well as Earth-S, Earth-X, and Earth-Four, should he be killed.
As his wave of destruction reached these universes, the Anti-Monitor manipulated The Monitor’s confidante, Harbinger, to kill her friend and inadvertently activated the towers.
In an attempt to destroy the towers, the Anti-Monitor sent his shadow demon legions to destroy them, but was thwarted by the united heroes and villains of Earth-1 and Earth-2.
Undeterred, after the Anti-Monitor managed to devastate Earth-S, Earth-Four, and Earth-X through manipulation, the heroes of Earth-1 and Earth-2 entered the anti-matter universe with the aid of Alexander Luthor Jr. and confronted the villain directly on Qward; with Supergirl (Earth-1) managing to damage his outer shell and destroy his primary citadel; albeit at the cost of her life.
While the heroes returned to the positive matter universe, believing the Anti-Monitor defeated and to mourn Supergirl's death, the Anti-Monitor simply repaired his outer shell and oversaw the completion of the Anti-matter Cannon, which would nullify The Monitor's towers and destroy the remaining five universes once and for all.
However, the Flash (Barry Allen), who had been kidnapped earlier due to his ability to traverse the Multiverse and brought to Qward for torture, managed to escape his bounds and, after inciting the Thunderers of Qward to rebel against the Anti-Monitor, entered the core of the Anti-matter Cannon and reversed the energy flow out of it; losing his physical form and becoming one with the Speed Force in the process.
Becoming frustrated, the Anti-Monitor decided to travel to the dawn of time and absorb the positive matter universe on the eve of its creation. As the villain was being stalled across time by the villains, the heroes, along with Superboy from Earth Prime, traveled to the dawn of time to stop him, however, it took the personal intervention of the Spectre; being backed up in power by the most powerful sorcerers of two Earths, to stop him.
However, the Anti-Monitor's meddling resulted in the remainder of the multiverse being condensed into two new universes (the positive matter and the anti-matter universes).
Enraged, the Anti-Monitor drew this new Earth into the antimatter universe, intending to destroy this last bastion of positive matter once and for all. What followed was the "Shadow Demon War", wherein many heroes and villains lost their lives against the Anti-Monitor's forces. Finally, the combined efforts of various superheroes and villains (Most notably Doctor Light (Kimiyo Hoshi), Alexander Luthor, Jr., Darkseid, Superboy, and Superman (Earth-2)) were able to weaken the Anti-Monitor enough for Superman (Earth-2) to deliver the final blow, destroying the Anti-Monitor and finally ending the crisis.
The Anti-Monitor's remains were later used as part of a tuning fork created by Superboy-Prime and Alexander Luthor Jr. in their bid to destroy the current Earth and create their own "perfect" Earth.
Ultimately, the tower was destroyed when Superboy, and Superboy-Prime crashed into it while fighting each other but, upon the resurrection of the Multiverse, the Anti-Monitor, along with his positive-matter counterpart, The Monitor, was also resurrected.
- The Anti-Monitor is the villain responsible for the Attack of the Anti-Monitor event. Noticing the time fluxes that were occurring on Earth due to The Councils battling to control the Nexus of Reality, the Monitor realizes that he could use the Nexus to eat an infinite amount of Earths. He is fought, momentarily defeated and sent to the future by The Flash and Professor Zoom in the Centennial Collapse 2017 event.
- Until the revamp of the anniversary event in 2021 the Anti-Monitor could be seen on top of the Science Spire overseeing the attack of his minions in the Metropolis Anti-Matter Invasion Zone.
- The Anti-Monitor is the final boss in the Doom: The Sixth Dimension 8-player operation.
- Players can obtain the Life Shell armor, the appearance of which is inspired by the Anti-Monitor.
- The Anti-Monitor first appeared in Crisis on Infinite Earths #4 (July, 1985).
- The armored "shell" that the Anti-Monitor now wears is actually a secondary shell he was forced to construct after nearly being destroyed by Supergirl (Earth-1) during the Crisis on Infinite Earths incident.
- The giant hand that Pariah and Krona witnessed when they respectively peered into the creation of the universe was the Anti-Monitor's during his attempt to alter the timeline to destroy the positive-matter universe.
- While the Anti-Monitor is not immortal, he may be ultimately indestructible so long as the Anti-Matter universe exists.