Anti-Monitor: ???? - Edit
Apparently the Monitor is the architect of the "Murums", which are barriers at the edge of reality which shape reality itself. Once he had finished construction of the metaphysical walls, the Monitor was free toshape reality as he saw fit witout outside meddling. Much of what Monitor created had been modeled on that which had been done before, but to conserve energy, the Monitor dialed down the powers of many powerful beings.
This measure was not enough, nor was a deal the Monitor made with a cosmic coalition knows as the Fanatics from Beyond.As he needed more power, the Monitor used Murums to make fundamental changes unique to our portion of reality; but as time went on, the Monitor became curious and sent scouts to travel through the Bleed, the substance between segments of reality, and tasked these scouts to investigate.
When the scouts returned with their reports, the Monitor found many of his scouts had been changed by the Bleed, giving them sentience and personality. An investment of the Monitor's own cosmic power, the scouts could pose a serious risk to reality if left to their own devices, the Monitor got creative and found a new purpose for many of the scouts, but some of the scouts were resistant to this and defied their creator and were punished.
Some scouts were destroyed outright and their tainted essence repurposed, but some scouts essence was too volatile to destroy. These scouts were locked away in a hastily built prison and sent far away until a cure could be found. Kept in such close proximity for too long, the combined taint of the Bleed began to fuse, pulling the imprisoned scouts together andreshaping them into a singular being forged by their shared hate of the one who had done this to them. Recently though an unknown means, the Anti-Monitor was freed from his prison.
After the Anti-Monitor's escape, he went into hiding and has now only in the last few months begun to step into the light. Interestingly, most sightings seem to place this being in South America, possibly being sheltered by the secretive criminal entityknows as the Cadre of the Immortal. Could the Cadre be a cult built around worshiping the Anti-Monitor? Scary thougth.