Set is the monstrous cobra-like God worshipped by the Serpent Men. He is pure deliberate evil, so wicked and despicable and mighty in magical power that virtually all the wizards of the world banded together to banish Set to the Abyss in order to protect the world from him.
He has ever since languished furiously in the Abyss, patiently awaiting the day when his Serpent Men worshippers free him so that he can terrorize and enslave the world and mankind once more.