By Rick Riordan
Hyperion

In this five-book fantasy series, protagonist Percy Jackson discovers he is the son of Poseidon, god of the sea, and that Greek mythology is no myth at all. At Camp Half-Blood, he learns that he is half-human and half-immortal, and being son of one of "the big three" (Zeus, Poseidon and Hades) makes him one of the most powerful demigods alive. Throughout the series, Percy and other demigods fight the monsters that are trying to take him down.