In Babylonian and Akkadian myth, Apsu, also known as Abzu or Apzu, is the primordial deity of the watery abyss and the deification of the vast primordial fresh water beneath the earth that serves as the source of all lakes, rivers, springs, streams and wells. He is the source of knowledge and was the lover of Tiamat, the primal goddess of the salt water, and together they created the gods in Mesopotamian mythology. His Sumerian counterpart is known as Engur.
In the Babylonian creation epic, the Enûma Elish, he was a primal being made of fresh water and a lover to Tiamat, a creature of salt water. Abzu could not quell the noise of the younger gods or their children. He colluded with his vizier Mummu to silence the gods and allow Tiamat to rest, after Tiamat rejected the idea. This resulted in the birth of the younger gods, who later murder Apsu in order to usurp his lordship of the universe.
He is also the name for fresh water from underground aquifers which was given a religious fertilizing quality in Sumerian and Akkadian mythology. Lakes, springs, rivers, wells and other sources of fresh water were thought to draw their water from the abzu.
"A Mesopotamian god of the deep waters. Apsu existed since the birth of time and is depicted as a freshwater sea. He is the source of knowledge and made the lands fertile. His fresh water mixed with that of Tiamat, the deification of the chaotic salt waters, and from there the main gods were born."
During the associated Vision Quest, the player must choose whether Naomi eliminates Tiamat or Apsu. If Apsu is confronted, upon his defeat he curses Naomi and kills her as he dies. The god's power is later absorbed by Manitou, which gives it strong physical attacks but a vulnerability to magical attacks.