Percy Jackson was the fearless Savior and Hero of Olympus. Key-word. Was. He was the retriever of Zeus's Master Bolt, sailor of the Sea of Monsters. He was bearer of the sky, wanderer of the Labyrinth, witness to the rising of Kronos, bearer of the Curse of Achilles, child of the first great prophecy, defeater of Kronos, Atlas, Iapetus, and Hyperion. He was Praetor of New Rome, helper in the freeing of Death, one of the Seven of the second great prophecy. He was survivor of Tartarus, defeater of Gaea and bane of monsters.
Now days, the story of Percy Jackson is just that: a story. A story that parents tell their children as a bedtime story to teach heroism and sacrifice. And everyone believes that it is just a story. Only a legend, because that is what the gods wished.
Because that's what happens to all the great heroes doesn't it? No-one believes that they really had the strength, or that someone made the hero up. Made up the story.
And thus, the truth of Percy Jackson, turned into just that. A legend.
Thysia of Chaos's army doesn't really have a history. Only his best friend, Anikitos knows his identity, along with Chaos himself.
No one under his command knows his real name, they only know that he was betrayed by the ones he loved and treasured most. No one knows which planet he was from, or what he did. Many have asked Thysia and Anikitos, but they never get an answer. Perhaps just extra training.
Thysia, as commander of the Army of Chaos, goes on almost every mission, no matter how small. When he has to go on a mission to Earth with Anikitos, the first mission to Earth he has been on in 250 years, he must save the planet from a great evil; the fated rising of the Primordials.