Erebus was the primordial being who represented the darkness of the underworld.
In Hesiod’s Theogony, Erebus emerged from Chaos alongside Nyx, the personification of night. Erebus embodied deep darkness or gloom, especially the shadowy region associated with the underworld. The name could therefore refer both to a divine personification and to a place or atmosphere of subterranean darkness.
Erebus and Nyx became parents of Aether, the bright upper air, and Hemera, the personification of day. This pairing reflects a recurring pattern in Greek cosmogony: contrasting forces such as darkness and light, night and day, arise from the earliest divine generations.
Erebus is often confused with Tartarus or Hades. Tartarus is primarily a cosmic prison or deep region below the underworld, while Hades can mean both the realm of the dead and its ruling god. Ancient authors sometimes used these names loosely, but Erebus most specifically denotes darkness or the dark passage associated with the underworld.