"Theogony" is a poem by Hesiod describing the origins of the Greek gods.
In the beginning, Chaos existed in the entire universe then gave birth to Gaia (Earth), Eros (Love), Erebus (Darkness), Nyx (Night) and Tartarus (Underworld).
The poem shows how the gods mated with each other to complete creation and from there where Greek mythology begins i.e. Zeus, Hera, Hades, Poseidon etc.