Gaia

Gaia (Γαία in Ancient Greek ) is the primordial Greek goddess personifying the Earth, and the leading antagonist of the second series, The Heroes of Olympus. She was the first being to arise from Chaos at the beginning of time. Her Roman counterpart is Terra. Terra is the Latin/Roman word for earth. Though sometimes presented as a maternal figure, particularly toward her Titan children, she can also be very cruel. In mythology she mainly exists as an enemy of the Olympians, sending Typhon and later the Giants to overthrow them. She is, however, ironically somewhat responsible for their rise to power.

History
Gaea and her husband and son Ouranos were two of the first Greek (gods, giants and titans) to emerge at the beginning of the world. She was the Primordial Personification of the Earth, and he was the Primordial Personification of the Heavens. They became partners, and brought forth the Titans, their children.
 * Oceanus
 * Coeus
 * Krios
 * Hyperion
 * Iapetus
 * Theia
 * Rhea
 * Themis
 * Mnemosyne
 * Phoebe
 * Tethys
 * Kronos

And The Hundred Handed-Ones She also consorted with Poseidon, Zeus, Tartarus, and Pontus.
 * Cottus
 * Briares
 * Gyges

By Zeus: By Poseidon: By Tartarus: By Pontus: Gaia also gave birth to the first Cyclops as well as the Hekatonkheires. She was also the mother of the Protogenos Pontus, the primordial personification of the ocean.
 * Kybele
 * Adgistis (faded)
 * Manes
 * Antaeus
 * Typhon
 * Echidna (though most say she was the daughter of Phorkys and Ceto)
 * Kampe
 * Giants (Gigantes)
 * Ophiotaurus
 * Aigaios
 * Nereus
 * Phorkys
 * Ceto
 * Thaumas
 * Eurybia

After Ouranos pushed the Hekatonkheires in Gaia's womb and the Cyclops into Tartarus, Gaia was furious. She asked her children to get rid of Ouranos 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 from Gaia's womb and the 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 banished Kronos into a place called Tartarus with bonds that they will never break.

Gaia's first attempt to avenge the titans was, with the spirit of Tartarus, giving birth to Typhon. Typhon, being the father of all monsters, was one of the worst enemies Zeus and the Olympians had to face. Typhon, with the help of Echidna, was able to render Zeus helpless and(because Zeus is immortal) imprison him in a cave. However, with the help of the other gods, Zeus, with his lightning bolts, was able to trap Typhon under Mt. Etna. Gaia then made peace with the Olympians and promised not to bother the Olympians again.

However, that was not Gaia's last attempt to overthrow the Olympians. She prophesied that Zeus's wife Metis would bear two children, first a daughter, and second a son who would eventually overthrow him. To avoid this fate, Zeus convinced Metis to transform into a fly, and then swallowed her. But it was too late. Metis already conceived a child. A few days later, Zeus received severe headaches. He convinced Hephaestus to axe his head open and out came a matured Athena. It is unknown if Metis escaped or not, but she never conceived the second child, so Gaia's plan, at least for a time, failed.

Some time later, Gaia used the Giants she has been harboring during the First Olympian War to avenge the Titans by attacking Mount Olympus, only for them to be defeated by the Olympian Gods and demigods.

The Battle of the Labyrinth
Gaia is mentioned by Annabeth in the Battle of the Labyrinth when Percy battles her son, Antaeus (Also a son of Poseidon), 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.

The Lost Hero
Gaia appears spirtually when Leo Valdez was little and leaving his mom's work and caused the place to burn down. Leo was alive because of his ability to resist fire, but his mom didn't make it out. So Gaia might have been very weak but beginning to wake, when Leo was little. Gaia also appeared during Jason's Quest to save Hera, speaking to Leo Valdez through a meduim of spilled toiled chemicals. It is officially revealed that Gaia is awakening and using the Giants to try and overthrow the current rulers of Olympus, the Olympians as she did after the First Olympian War.

Personality
In many ways, Gaea is the ideal mother, loving her children first and foremost. She will do anything to protect them, even if it means taking the most extreme measures. It is because of this protectiveness that she is known to be very cruel to anyone who threatens them.

Powers
Gaia is the eldest of all the Primordial gods, goddesses, Titans, and Titanesses. Being the all-encompassing Mother 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. In The Lost Hero it's said that if she were to rise in her full physical form she would be more terrible and powerful than any other force on the living planet. She may have some power over the Underworld as she was able to bring many back from the dead by opening new exits out of the underworld.