Percy Jackson and the Olympians: Legends

She has the shape of a woman of great size, with the body of the color of the sea, and from its back, arms and legs hang several fins.

Lamia is an ally of Poseidon, the God of the Seas. Lamia had attracted the attention of Zeus and accepted his courtship. But upon doing so, faced the wrath of the jealous Hera. Hera killed her children, Altheia and Demetrius, and then Lamia was turned into a monster. Angered at the goddess, she used an incantation to allow all the monsters in the world to sense the taint of half-bloods, so that they could always be found. Lamia did it out of spite so that Hera would finally understand her pain of losing her family after so many demigods have been killed.

Lamia is returned to life by Gaea, who sent her to kill Alabaster C. Torrington, another child of Hecate. Alabaster tried to kill her several times, but because Gaea has opened the Doors of Death, and also because Thanatos was chained by Alcyoneus, Lamia wouldn't stay dead - she would just turn to black dust and reform within minutes. After a speech given by Howard Claymore about his new book (the sponsor of which is Lamia), she notices Claymore and Alabaster interacting and pursues Claymore, only to discover later, he's an ally of Alabaster. She curses Claymore after their brief encounter, which shatters the protective magic Alabaster cast to shield himself from Lamia. But with Claymore's help, Alabaster discovers an incantation that will bind Lamia to the Earth. However, their mutual mother, Hecate, steps in to intervene, saving both her children due to her desire not to lose any more of them after so many perished in the Second Titan War.