In Greek mythology, Chaos (Greek: Χάος), according to Hesiod, Chaos ("Chasm") was the first thing to exist: "at first Chaos came to be" (or was) "but next" (possibly out of Chaos) came Gaia, Tartarus, and Eros (elsewhere the son of Aphrodite). Unambiguously born "from Chaos" were Erebus (Darkness) and Nyx (Night).
The Greek word "chaos" (χάος), a neuter noun, means "yawning" or "gap", but what, if anything, was located on either side of this chasm is unclear. For Hesiod, Chaos, like Tartarus, though personified enough to have born children, was also a place, far away, underground and "gloomy", beyond which lived the Titans. And, like the earth, the ocean, and the upper air, it was also capable of being affected by Zeus' thunderbolts.
For the Roman poet Ovid, Chaos was an unformed mass, where all the elements were jumbled up together in a "shapeless heap".
According to Hyginus: "From Mist (Caligine) came Chaos. From Chaos and Mist, came Night (Nox), Day (Dies), Darkness (Erebus), and Ether (Aether)." An Orphic tradition apparently had Chaos as the son of Chronus and Ananke.
In Aristophanes's comedy Birds, first there was Chaos, Night, Erebus, and Tartarus, from Night came Eros, and from Eros and Chaos came the race of birds.