Tharizdun is an ancient being of immense power. He is alternately known as “the chained god,” or “the mad god.” His symbol is a jagged spiral.
According to Heirmus: "Before our gods ruled this mortal plane, before mankind existed, there was a group of powerful beings known as the Primordials. They were little more than directed chaos, and no life could thrive in their capricious wake. Our gods eventually cast them down, but just before the end, when it was clear that the Primordials would be defeated, one of the gods betrayed the others. Tharizdun went to the nearly-extinguished Primordials and bargained with them. He took some of their power, and became stronger than all of the other gods combined… or so he thought. In truth, the gods recognized the shared threat and banded together, Pelor fighting next to Asmodeus, Corellon fighting next to Gruumsh, Tiamat and Lolth with Moradin and Sehanine. With their shared power, they locked Tharizdun in chains. But now, the threat secured, they returned to their mistrust of the others. And so they agreed to build a “weapon” that would send Tharizdun farther than any of the gods could reach, out of this plane and all the other known planes. Of course, they did not trust each other to keep it. So they split the weapon in four pieces, and scattered it… or so it seems. The bit about the ‘sending Tharizdun away’ is spotty."