Phaedra was a legacy and a queen of Athens, former princess of Crete and wife of Theseus.
Percy Jackson's Greek Heroes
After Theseus slayed the Minotaur, she joined Theseus, her sister Ariadne, and the surviving Athenian tributes on their quest back to Athens. Along the way Theseus and Ariadne has a falling out and he left her on an island and started a relationship with Phaedra soon after.
They eventually married and she lost interest in Theseus and found new romantic feelings towards her step-son Hippolytus. When Theseus found out he had his son killed by gods.