Background: A primordial god of the the flames that blaze in the void. Algol was both the god of stars and demons. Coming from the Supernal, his true nature is beyond mortal comprehension. He was cast down when the Exarchs ascended to the heavens. With the shattering of the Ladder and the destruction of Atlantis, he was trapped and bound in the world.
The Circle of Four discovered the wounded god and built a more perfect prison over his dormant form. They found an ancient vampire called the Antediluvian and enhanced it with the power of one of the Idigam. This composite being would destroy encroaching civilizations before their festering evil could release the god. Then they bound a potent spirit of lies called Nehjarra to ensnare the unwary and lead smaller civilizations into a spiral of destruction. They molded the landscape with potent magics accessible only in the supernal and cast their messages into the future so that their agents could maintain the prison for all time.
But Algol stirred. Its allies burned cities and murdered entire cultures in order to upset the balance of its prison. Others sought to use its escape as a doorway to the Supernal. In the end the release was dangerous and doomed several parallel worlds. But chicago was saved and the supernal altered. What this means is unclear.