Protogenos

The Protogenoi, in Greek mythology, were the first beings that came into existence before the universe was created. A great deal of them were not actually envisioned by the Greeks as having solid forms; instead, they were mainly personifications of their roles in the universe. The first of the Protogenoi was Chaos, who represented the endless void of nothingness that existed before the universe was created. The most well-known of the Protogenoi was Gaea, who represented the earth. Her son and husband Ouranos represented the sky. The Protogenoi were eventually overcome by the Titans, although since they were personifications of things that could never be destroyed (earth, darkness, etc.) they never really faded. Ouranos was killed by his son, Kronos, and the others, such as Gaea, were merely put to 'sleep' for eons.

The Heroes of Olympus
Gaea, the Protogenos of the Earth, is the main antagonist of the series. Much like Kronos in the first series, she and her children, the Gigantes, are working to destroy the gods; however, they plan on destroying the original Mount Olympus in Greece, the gods' roots, since that is where the gods' power is truly held.

List of Notable Protogenoi

 * Chaos - Protogenos of the Universe
 * Erebos - Protogenos of Darkness & the Underworld
 * Nyx - Protogenos of the Night
 * Aether - Protogenos of Light
 * Hemera - Protogenos of Day
 * Thalassa - Protogenos of the Sea (or the Sea's surface)
 * Gaea - Protogenos of the Earth
 * Ouranos - Protogenos of the Sky
 * Pontus - Protogenos of the Sea
 * Ourae - Protogenoi of Mountains
 * Nesoi - Protogenoi of Islands
 * Tartarus - Protogenos of the Pit
 * Chronos - Protogenos of Time (often confused with the Titan Lord Kronos)
 * Anake - Protogenos of Necessity and Inevitablility (Fate)
 * Physis - Protogenos of Nature (order and origin of nature)
 * Phanes/Eros - Protogenos of Procreation/generation (differs from Eros, the godly son of Aphrodite)
 * Thesis - Protogenos of Creation
 * Hydros - Protogenos of Water