Nyx, the daughter of Chaos, being the personification of Night, was, according to the poetic ideas of the Greeks, considered to be the mother of everything mysterious and inexplicable, such as death, sleep, dreams, etc.
She became united to Erebus, and their children were Aether and Hemera (Air and Daylight), evidently a simile of the poets, to indicate that darkness always precedes light. Nyx inhabited a palace in the dark regions of the lower world, and is represented as a beautiful woman, seated in a chariot, drawn by two black horses.
She is clothed in dark robes, wears a long veil, and is accompanied by the stars, which follow in her train.
From: Berens, E.M. The Myths and Legends of Ancient Greece and Rome. New York: Maynard, Merril, & Co., 1880. Text in the public domain.