The Lightning Thief is a 2005 fantasy-adventure novel based on Greek mythology. It was the first young-adult book written by author Rick Riordan. It is the first book in the "Percy Jackson & the Olympians" series. The series is about the adventures of modern 12-year-old Percy Jackson after he discovers he is a demigod (half-human, half-god). Percy is the son of a mortal woman and the Greek god Poseidon. Percy and his friends go on a quest (adventure) so that a war between the Greek gods Zeus,