Billiions of years ago, many refugees from the First Gods took up residence in a pre-sentient expanse of space. Rich in magical energy and close to many 'thin' points in the dimensional walls of the multiverse, the entity was not unwelcoming of the new residents and they grew a symbiotic relationship with it. Called the Demiurge, it became a new home for the so-called Elder Gods who dwelt there.
Among those gods was Gaea and her brother Chthon. Millions of years before humanity would even start using tools, a terrible war raged among the Elder Gods. Many of them degenerated into demons and monsters of nightmarish composition. Gaea bonded with the nascent energies of the Demiurge and produced Atum. Atum was tasked with preserving the balance of the godheads and systematically killed and banished many of the survivors. Only a few survived his wrath by slipping into sub-dimensions and claiming them as their personal demesne, such as ancient Chthon.