The Percy Jackson Series is a popular fantasy book series written by Rick Riordan. It follows the adventures of a young boy named Percy Jackson, who discovers he is a demigod, the son of Poseidon, the Greek god of the sea. The series blends modern-day life with elements of Greek mythology, as Percy and his friends embark on quests to save the world from various mythological threats. The series consists of five main books, starting with "The Lightning Thief" and concluding with "The Last Olympian." It has gained a large following and has been adapted into movies and graphic novels. The success of the series also led to spin-offs, including the "Heroes of Olympus" and "Trials of Apollo" series.