Earth-51

Earth-51 is the official nomenclature used to describe a fictional reality featured in comic books published by DC Comics. It first appeared in Countdown to Final Crisis #19 in December, 2007.

History
Earth-51 is one of fifty-two divergent realities that branched from the core New Earth reality during the recreation of the Multiverse shortly following the events of Infinite Crisis.

The history of this Earth is unknown. However, it was quite similar to Pre-Crisis Earth-One: Barry Allen is the Flash, for example. At some time in the past, the Jason Todd of this world was killed by the Joker. Enraged, Batman killed the Joker, and this event pushed him over the edge. He began targeting supervillains, and his strategic mind allowed him to succeed where so many had failed. Unaware of his actions, the other superheroes reacted to the disappearance of their nemeses by revealing their secret identities and becoming more publicly accepted. Through their efforts, wars were stopped, famines averted and humanity entered a golden age.

However, this state of perfect peace made the world a perfect target for Monarch and his pan-universal army. After the retired heroes were killed by their evil counterparts in a series of coordinated strikes, Monarch's force came through in Metropolis. However, they were opposed by the combined forces of the Monitors. After deaths on both sides, the Monitors pulled back to their stronghold to make room for Superman-Prime. Attacking the invaders, Superman-Prime punched Monarch so hard that his armour ruptured. The resulting quantum event destroyed most of this reality, leaving one plant sprout and this reality's Monitor: Nix Uotan. Encouraged by the survival of the plant, Nix Uotan vowed to rebuild reality.

When Nix Uotan rebuilt Earth-51, he decided to make it similar to New Earth, whose heroes had been able to hold off the forces of evil and chaos for years. However, out of deference to their role in the previous Earth's destruction, this Earth had no equivalents of Ray Palmer, Kyle Rayner, Donna Troy, Jason Todd, Holly Robinson, Harley Quinn, Jimmy Olsen, Karate Kid and Triplicate Girl. This version of Earth-51 survived until the New Earth heroes returned in the mistaken belief that it was New Earth.

However, Karate Kid had been infected with the Morticoccus virus, and was soon going to die. When he died, the virus spread out from his corpse, circumventing STAR Labs and Cadmus biohazard protocols and spreading to the general population. Although the scientists managed to create a vaccine, the virus had spread too far for it to be useful.

The virus scrambled the DNA of its victims, mutating lifeforms across whole species before killing them. Heroes, villains and citizens all over the world were transformed into maddened human-animal hybrids. Meanwhile all the animals of the world began to gain intelligence, and banding together in the chaos, eventually they gained power in the dying world.

The last superheroic survivors of this world escaped into the Multiverse with the Challengers from Beyond, leaving Una, Buddy Blank and his unnamed grandson behind. Una sacrificed her life so that Buddy could save his grandson in the secure Command D bunker. As he tucked the boy in, Buddy remarked that he hoped his grandson would forgive Buddy for making him "the last boy on Earth".

Nothing is known of events on the Earth after this point, except that, at the beginning of the Final Crisis, the universe of Earth-51 had been removed from real-space from under the Monitors' watch.

Upon being removed from realspace, Universe Designate 51 became part of Limbo. Onto its surface washed the forgotten characters of the multiverse as well as fragments and devices from the other 51 worlds. The lost characters formed the Court of Limbo, under the leadership of Merryman.

Sometime after its removal from reality, Earth-51 became home to the Library of Limbo, an artifact in the rough form of the book, which contains an infinite number of pages.

This world was the site of the crash landing of the Ultima Thule, and was subsequently attacked by the colossal minions of Mandrakk the Dark Monitor.

In the throes of the Final Crisis, the forces of Checkmate used advanced technology to initiate the Black Gambit: to move a portion of New Earth's population to a safe haven in an entirely different universe - Earth-51. After Checkmate succeeded (with help from the Super Young Team and Mister Miracle), the Judge of All Evil used his new powers to remove all the elements relating to the Final Crisis - the New Gods of the Fourth World, Kalibak's tiger-soldiers, the Morticoccus virus - from new Earth's history and create a new history for Earth-51 out of them.

Checkmate, now reformed as the Global Peace Agency of Earth-51, is using OMAC units and agents with the Question's mask to maintain order on a world where humanoid animals have large empires, primal gods battle for dominance... and the Last Boy on Earth is set for the adventure of a lifetime.