Leto

Leto (Ancient Greek: Λητώ) is a daughter of the Titans Koios and Phoebe and the sister of Asteria. Through Zeus, she is also the mother of Apollo and Artemis.

History
Through the King Zeus, Leto is the mother of Apollo and Artemis. When she was pregant with the twins, she was pursued relentlessly by the goddess Hera, who drove her from land to land preventing her from finding a place to rest and give birth. The floating island of Delos eventually provided her with refuge. Later when she was later travelling to Delphi, the giant Tityos attempted to abduct her, but Apollo intervened and slew him with arrows.

The House of Hades
Leto is mentioned by her father Koios, who claims his daughter would likely fight for vengeance, alongside the Titans after the way Zeus treated her.

Trivia

 * Leto makes her only appearance in Percy Jackson's Greek Gods, though she is mentioned in The House of Hades.