Abaddōn first born son of Poseidon and Hestia was born after the 1st Titan War. After the Giant War he vanished from the world, after single handedly defeating Gaia and her son Typhon father of monsters. When he disappeared he left everyone in a state of fear and aghast. He also left behind a heart broken goddess of the moon. But when he returns he is no longer know as Abaddōn but as Perseus Jackson.
Copyright Disclaimer: I do not own the Percy Jackson book series or the Heroes of Olympus they belong to Rick Riordan.