Chaos

Chaos, was the first thing that existed. According to Hesiod, "at first Chaos came to be...but next," came Gaia, Tartarus, and Eros. Unambiguously born from Chaos were Erebus and Nyx.

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 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".