The mutants and the Avatar

Super-powered mutants first appeared in the 1920s: Various boys and girls, more-or-less evenly distributed among populations, began manifesting metahuman abilities as they reached puberty. The phenomenon was completely mysterious at the time; in the modern era, thanks to the progresses of physics, biology, and genetics, the mechanics of mutation are somewhat more clearly understood - but its actual cause remains unknown. It is widely agreed among the scientific community that there is genetic engineering at work, modifying human fetuses to give them powers...but the nature and identity of the engineer is a complete mystery.

Whatever the cause, the mutants were here, and their powers were more than enough to cause great worries. Fear was rising, and could probably have led to chaos, had it not been for the Avatar:

Not long after the mutants first appeared, the Avatar made his first appearance. Dressed in a white-and-gold costume, wearing a cape, radiating faint light, and wielding cosmic powers so great as to dwarf those of the mutants, the Avatar embarked on a campaign of heroics across the world, putting out fires, rescuing people from accidents, saving communities from natural disasters, fighting crime, and generally being a protector of humanity 24 hours a day, 7 days a week (literally. The Avatar has never been recorded taking a break, not even to eat or sleep).

On one hand, the Avatar proved even more frustratingly mysterious than the mutants, refusing to answer any questions concerning his true nature and origins, or even why he called himself "the Avatar". On the other hand, his charisma and heroics soon made him an inspiration to many; both to regular humans, who learned thanks to him not to fear super-powered individuals, and to a large segment of the mutant population, who began to see him as a role model: In the years that followed, many mutants opted to follow his example, using their powers for heroics.

The Age of Superheroes had begun.