Typhon

Typhon (or Typhoeus) is the last child of Gaea. He is the god wind and known as the "Storm Giant" or "Father of all Monsters." His wife is Echidna.

History
Thousands of years ago, after the First Olympian War, Gaia was enraged at the defeat of the Titans, her children. She attempted revenge by sending her last and most powerful child, the great monster Typhon to destroy the Gods. Typhon alone is the greatest foe the Gods ever faced, even mightier then the Titans themselves.

Having never anticipated such a rival, the Gods fled. Zeus however, gathered his courage and stood his ground. He refused to give up even though he could barely hold his own. The Gods, inspired by Zeus' actions, aided their brother against Typhon. Even with their combined efforts, they could not kill Typhon. However, they were able to trap him in Mt. Etna, where his raw power itself causes lava to ignite from the mountain top in the form of a volcano. After the defeat of her most powerful child, Gaia admitted defeat and allowed the Gods to rule Olympus without interference.

Western Civilization
When the Gods moved to the western civilization, Typhon's life force was tied to Mount Saint Helens. Like in Mount Etna, his raw power ignites lava from the mountain top. Though he was succcessfully imprisoned for thousands of years, his prison could not hold him forever. During his efforts to kill a gang of Telekhine, Percy was forced to call on all of his power to escape Mount St. Helens. It was this that weakened the seal on Typhon's prison and awakened the Father of All Monsters. It was soon that Typhon would rise again to finish what he started... destroy the Gods.

The Last Olympian
It is in the final book that the inevitable finally occurs. Typhon escapes in a catastrophic explosion of Mount St. Helens. Following his escape, Typhon heads to New York. Using the Mist, Typhon is able to conceal his true form from the mortals and appears as a freak storm. The Gods are unable defeat him as Poseidon is occupied defending his undersea kingdom and Hades refuses to fight. The Titans themselves use While the Gods are busy fending off Typhon, the Titans made their way to Mount Olympus, which was being defended by Half-Bloods.

Percy prays to his dad and asks him to leave his kingdom and come to help the Olympians defeat Typhon. His father agrees and when Typhon steps into the East River, the call of the ocean is heard and Poseidon rides into battle along with Tyson and his brethren cyclops'. They chain him, and Posiedon opens a slide to Tartarus and casts Typhon down.