Percy Jackson is a demigod, the son of the mortal Sally Jackson and the Greek god of the sea Poseidon. He has ADHD and dyslexia because of his battlefield reflexes and because his mind is hardwired for Greek. He has been expelled from almost every school he has ever attended. He is 12 years old in The Lightning Thief, and is a year older in each subsequent book until he is 16 in The Last Olympian. Like other half-human half-god demigods, he is expected to act as the Olympian gods' agent in the mortal world, taking action where ancient laws forbid direct godly intervention, usually in the form of quests. His personality is described as "changeable"(like the sea) and hard to predict with the exception that he is very loyal to his friends and family. His powers, which start small and develop as the books proceed, include controlling water, making hurricanes, breathing underwater, and talking to horses, Pegasi and fish. He also becomes an accomplished sword-fighter and leader, as well as being the leader of the Poseidon cabin at his demigod camp, Camp Half Blood.
Percy Jackson's fatal flaw is loyalty, which he at first questions how it can be a weakness, but then seems to accept it and try to not let it control him. Throughout the rest of Percy Jackson & The Olympians, Percy grows more confident and courageous. He overcomes several obstacles that have been thrown at him to keep him from saving the world. The Blood of Olympus ends with Percy and Annabeth planning to finish senior year in New York before heading to the college in New Rome.