According to Hesiod and his work Theogony, the first deity out of which the rest emerged was Chaos. Out of Chaos jumped Erebus (darkness), Aether (light), Nyx (night), Hemera (day), Tartarus (the underworld) and Eros (procreation). The primordial gods were usually depicted as places or realms, as can be seen from the above. Gaea (mother Nature or earth) was also a daughter of Chaos, along with Uranus (heaven) and Pontus (sea).
The union of the primordial deities Uranus and Gaea gave birth to the Titans, who ruled during the Golden Age. The Titans were Cronus, Oceanus, Hyperion, Coeus, Crius, Iapetus, Mnemosyne, Tethys, Theia, Phoebe, Rhea and Themis. Cronus became the ruler of the gods after dethroning his father Uranus, but was later dethroned himself by his son, Zeus.
During the era of the Olympians, other deities were also in existence alongside the twelve well-known gods. Some examples include the numerous nymphs and deities of the forests, the seas and the rivers, demi-gods such as Heracles and Theseus, and many others that represented every possible aspect of the life and the surroundings of ancient Greeks.