Tharizdun
From Syra D&D Wiki
Tharizdun is a powerful being who was locked away by the other gods, good and evil alike, at the dawn of the world. The location of his prison has long since been forgotten, and even his nature is the stuff of legends: there are some who worship him as a god, some who see him as the greatest of the primordials, and a few who believe him to be both. What is known is that he desperately desires a release from his eternal prison, and were he to succeed the results would be disastrous.