Apep

Apep, King of Serpents, is the deadly enemy of the Egyptian Pantheon. Resembling a colossal fiery serpent, it is the embodiment of chaotic evil in that mythos; it has no creed but destruction. It is served by flame+snakes and has a few clerics among dragons, nagas, and yuan-ti; its human followers disguise themselves as ordinary members of society.

Currently, Apep is imprisoned in the Wells of Darkness, guarded by a gargantuan six-armed construct. Each day, worshippers of the pantheon intone passages from the Books of Overthrowing Apep, conpendia of true names, mutilation rituals, and power-draining incantations designed to keep it locked away forever.