Erebus is one of the primorials in greek mythology, he was born out of the void. He was the offspring of chaos and brother of the other primorials including Gaia(earth), Tartarus(underworld), Eros(love), and Nyx(night). He was identified as one of the first 5 beings to exist. Erebus is the primordial of darkness, consort of Nyx. He was the father of Aether(The upper atmosphere), Hemera (Day), Hypnos(sleep), and moirai( the fates).
Some legends described him as the lower part of the earth where he was believed to be Hades or part of Hades. Erebus was believed to be the upper part of the underworld while tartarus was the lower half, he was the part where souls immediately went after dying.