After the Cataclysm
Before the creation of the many worlds, ancient powerful beings called the weavers created and experimented on other worlds, nurturing life and observing it, studying and researching in their vast citadels full of books.
In a hidden chamber, far from these citadels, one of the weavers was set with a single task: to guard the entrance to the chamber that held the only book they must not read, must never open. No one knows how long the keeper of the book stood watch before they walked into the chamber and opened the book. We know only that eventually they did.
When the book opened, darkness and horror entered the world. The weavers and their worlds fell and died, one after another, and they fled, somehow, and created the many worlds. They created the primordials to help them to create new worlds and peoples, and they built devices and structures designed to defend the worlds against the terrible powers that followed them.
Eventually, most of the weavers died, but their creations lived on, and the inhabitants of the many worlds were left under the influence of incomprehensible, cruel, and mad gods.