The Percy Jackson Series, written by Rick Riordan, follows the adventures of a young demigod named Percy Jackson, who discovers he is the son of Poseidon, the Greek god of the sea. The series begins with "The Lightning Thief," where Percy learns about his heritage and embarks on a quest to prevent a war among the gods. Throughout the series, Percy and his friends, including Annabeth Chase and Grover Underwood, face various mythological challenges and monsters. The books blend modern-day life with ancient Greek mythology, making them engaging for young readers and fans of fantasy literature.