She was the companion of the God, and together they crafted Man; however even in those days Her envy was great, and she sought to use their creation against the God, and so for Her sins she was cast into the Abyss.
The Dark Mother raised above Man 13 disciples, and gave unto them the gift of Death Everlasting, and in those days she said unto them, go out into the world and spread the Truth of my return, that Man might fear and the very foundations of Heaven might come loose.
Undead goddess motivated solely by her hatred of the god, first she raised up the dead to walk the earth as her slaves, primarily to build her a tower of babel so that she might personally storm the gate of heaven and wreak vengance on the god.
In the beginning of the world she was bound to her tomb deep under the earth, and was wracked eternally by the fires of hell. until at last she tricked some cabal or another to release her from her prison for some pretty lore or another. she remained bound for a while longer, with chains of magic, and served mankind as a sort of enslaved tutor.
when she finally broke her chains the sun set on the world for the last time, the dead rose and she began slaying all those who bound her. with the night came the cold, and the hunger, and in those first days many that had fled originally came and sold themselves or their family to the dark mother, to serve as sources of blood and slaves of her vampiric servants.
ephraim took his disciples underground and founded teh church to fight the dark mother. ephraim possibly one of the ones who binded her, at least according to apocryphal sources, though to say that is to bring down the wrath of the faithful upon yourself.