An adolescent metahuman

On Megacrossover Earth, metahumans are defined as humans possessing mutations that give them and their descendants superpowers. They are often also referred to as "mutants" and "mutates", although those words are considered offensive to super-powered humans. There are many different variants of metahumans, but common traits are enhanced intelligence, strength, and speed.

The most common source of metahuman traits is the meta-gene, which was granted by Gaea to prehistoric humans to protect their world from hostile outsiders. Normally, the meta-gene lay dormant, but it could be activated upon a moment of extreme physiological stress. In some rare cases, it was activated purely spontaneously. Before the twentieth century, active meta-genes were rare. Those who had their meta-genes activated were often believed to be witches or demon-spawn and were feared by baseline humans.

During the late nineteenth century, Professor Abednego Danner created a super-serum that activated a person's meta-gene. He used it on his firstborn child, Hugo, who developed superhuman strength and agility. When Hugo enlisted in the First World War, he donated samples of his blood to the US Army. By the end of World War II, all major Allied military forces were creating super-soldiers.

After the war, the soldiers had offspring who carried developed their own abilities around puberty. The growing number of metahumans was seen as worrisome for the general populaces. In Soviet Russia and Maoist China, all metahuman children were declared wards of the state and raised in special camps apart from their parents. Those that did not pledge total loyalty were killed.

In the United States, Britain, and France, the governments chose to wait until the super-soldiers' offspring reached maturity. Some of the super-soldiers and other metahumans elected to set up special schools to train metahuman children. However, an alarming number of the young metahumans believed that they were superior to baseline humans and were not afraid to use violence to pursue their own agendas. The U.S. government eventually responded by passing the Metahuman Registry Act in 1984.