The Story of the Precursors

For those who are unfamiliar with lore from the Halo Universe, this may be a bit confusing.

The Precursors were ancient beings, almost God-like, who had the ability and technology to create, and accelerate the evolution of intelligent life.

These are the creatures that created the Forerunners and Humanity. They had a philosophy, called the Mantle, which the holder of the Mantle had the responsibility to keep peace and preserve the biological diversity within the galaxy.The precursors eventually wanted to pass this responsibility to one of their creations, as their legacy. They chose the humans for this fate The Forerunners found out about this, and wanted the Mantle to be their responsibility, as they saw themselves as superior. The rose up against their creators and ruthlessly annihilated them and drove them to (near) extinction, so they could seize the mantle for themselves. As a fail safe, the last remaining precursors transformed themselves into a powdered dust forms, which could be later revived into their former selves. But after eons of waiting, the dust became flawed and corrupt. When ancient humans found the dust, (prehistoric humans were an extremely advanced, space faring race before they lost  the Human-Forerunner War and were devolved by the Forerunners), it had become the cancerous plague we now know as the Flood.



So there we have it, the mystery of the origins of the Flood are no longer mystery. The Flood, all this time, had been perverted, insane, remains of what was left of the ancient Precursors.