Erebus was known as the embodiment of primordial darkness, the
son of Chaos
(who was the void from which all things developed, known also as Darkness). According to Hesiod's Theogony
, Erebus was born with Nyx
(Night), and was the father of Aether
(the bright upper atmosphere) and Hemera
, the ferry-man who took the dead over the rivers of the infernal region, is also said to be the son of Erebus and Nyx.
Later legend describes Erebus as the Infernal Region below the earth. In this version, Hades was split into two regions: Erebus, which the dead have to pass shortly after they have died, and Tartarus, the deepest region, where the Titans were imprisoned. Aristophanes' Birds says that Erebus and Nyx were also the parents of Eros, the god of love.
He is often used metaphorically for Hades itself.