List of Percy Jackson and the Olympians characters
Nico di Angelo: A son of Hades. When his sister Bianca dies, he blames Percy and vows revenge. In the fourth book, Percy sees an Iris message from Bianca of Nico talking to a spirit while in the Underworld. Nico returns at the Triple G Ranch and then leaves it to avoid Percy and friends, from whom he has just discovered were not responsible for the death of Bianca. He comes back again and saves Percy, Rachel, Grover, Annabeth, and Tyson from Kronos, the Lord of Time. Doing this, Nico exposes the fact that his father is Hades, making him vulnerable; Kronos will try to bring him to his side because he is a son of one of the Big Three. He also fights in the Battle of the Labyrinth, leading an army of ghostly soldiers, but later disappears after noting that he is not welcomed at Camp Half-Blood, much like his father is not welcomed at Olympus. He reappears several months later and informs Percy of a plan that could lead to sending Kronos back to Tartarus. In the final book, he convinces Percy to bathe in the River Styx, making him undefeatable, but not before taking Percy to Hades in exchange for information about his mother. He later rescues Percy, and convinces his father Hades to help defend Olympus.