Aredhel

Warning: Wikipedia contains spoilers

She was tall and strong, fond of hunting and riding in the forests. Her skin was pale and her hair dark; she always wore silver and white. Though fond of the sons of Fëanor, she never fell in love with any of them.

After arriving in Middle-earth, she dwelt in Nevrast[?] with Turgon, and went with him to Gondolin. But after two hundred years the longing for the forests and wide lands overcame her, and she asked leave to depart. Turgon was unwilling, fearing the exposure of the Hidden Kingdom, but eventually relented.

Riding with companions, they were denied entrance to Doriath, it being closed to the Noldor, and so they went around to the north, where she was separated in the dangerous region of Nan Dungortheb[?] and reported lost. But she reached Himlad[?] safely, and waited there to meet Celegorm[?] who was abroad, but eventually she wandered out of boredom, and became lost in the forest of Nan Elmoth.

Eöl the Dark Elf ruled those woods; they met, and he led to his home, where she stayed for many years, and were married. They had a son named Maeglin, and telling him of her former life and home, she desired to see them again, and left Nan Elmoth with Maeglin while Eöl was away. They reached Gondolin (not realizing that Eöl was following them all the while), and were received with rejoicing. Eöl was also discovered and brought before Turgon, but rather than accept Turgon's judgement, he attempted to kill his son. Aredhel stepped in front of the stab, but because it was a poisoned dart, she died that night from the wound.

Eöl was cast down from the city walls and died, while Maeglin became mighty in Gondolin and later betrayed it to Morgoth.