Nyx was the Greek primordial goddess. She was the essence of the night whose sons were the twin brothers Hypnos, the god of sleep, and Thanatos, the god of death. In another legend Nyx was the feminine power that coexisted with the amorphous male power, Chaos, before cosmic creation. A.G.H.
Jordan, Michael, Encyclopedia of Gods, New York, Facts On File, Inc. 1993, p. 190