Gaia

Gaia (Γαία in Ancient Greek) (sometimes spelled Gaea) is the primordial Greek goddess personifying the Earth. She was the first being to arise from Chaos at the beginning of time.

History
Gaia and her son Uranus were two of the first Greek gods to emerge at the beginning of the world. She was the goddess of the Earth, and he was the god of the Heavens. They became partners, and brought forth the Titans, their children.
 * 1) Oceanus
 * 2) Koios
 * 3) Krios
 * 4) Hyperion
 * 5) Iapetus
 * 6) Theia
 * 7) Rhea
 * 8) Themis
 * 9) Mnemosyne
 * 10) Phoebe
 * 11) Tethys
 * 12) Kronos

And The Hundred Handed-Ones
 * 1) Kottos
 * 2) Briares
 * 3) Gyes

Gaia also gave birth to the first Cyclops as well as the Hecatonchires. Along with them, she was also the mother of the Protogenos Pontus, the primordial personification of the ocean. She also fathered many of his children, as well as children of the Olympians and other Protogenoi. She is also the mother of the monster Typhon, whom she bore through a coupling with Tartarus.

After Uranus threw the Hekatonkheires and Cyclops into Tartarus, Gaia was furious. She asked her children to get rid of Uranus so she could save her other children, and only Kronos was brave enough to do it. He took a scythe Gaia made, and got rid of his father.

However, Kronos didn't rescue his brothers, and Gaia was then angry with him. Gaia then prophesied that Kronos in turn was destined to be overthrown by his own son, and so the Titan attempted to avoid this fate by devouring his young. Zeus, through deception by his mother Rhea, avoided this fate, and later rescues the Hekatonkheires and Cyclops from Tartarus, and forced his father to vomit up his brothers and sisters.

A war then started between the Titans and the gods, Hekatonkheires, and Cyclops. The young gods emerged victorious, and cut Kronos into a million pieces, with his own scythe, and tossed what was left of him into Tartarus.

The Battle of the Labyrinth
Gaia is mentioned in the Battle of the Labyrinth when Percy battles her son, Antaeus, in an arena deep within the Labyrinth. At first Percy is unable to harm him, because any wound he receives is instantly covered by sand and healed by Gaia's power. Percy is able to defeat him by causing him to be disconnected with the Earth, rendering his mother unable to protect him.

A river nymph also mentions her when she tells Percy that the area around her river, including Geryon's stables, were once part of the ocean when only Gaia and Uranus reigned. This references the first age of the world, before the Titans ruled.

Personality
Gaia is the mother of the Titans, and the grandmother of the gods. She loves her children very much, and was furious with Uranus for throwing them in to Tartarus, even willing to give up having more to save them, only for Kronos to conduct a similar act with his children. After the Titanomachy, she also sent her greatest son, Typhon, to war with the Olympians. As well, she also instigated the Gigantomachy, in which she persuaded the Gigantes to rise up against the Olympians. So, in retrospect, she is responsible for the usurpation of her husband and for two attempts on the Olympians.

Power
Gaia is the eldest of all the goddesses. Being the all-encompassing mother of earth she can manipulate the earth and sense everything that occurs on or within it. She does not appear physically in the series, so her exact influence and powers are mysterious. Mythology presents Gaia as seldom taking a physical form, her spirit instead remaining within the Earth itself.