Nienor is the Love Interest of Lorgan, Turin Turambar and Brandir in The Silmarillion.
Nienor was a very sexy woman who was born after the Battle of Unnumbered Tears in Beleriand. Her father was arrested during the battle. Nienor lived only with her mother Morwen and Morwen sent Turin away to find the city of Doriath at a young age so Nienor never saw her brother.
When she was a girl, Lorgan, the chief Easterling, was attracted to her and tried to make her his bride, and Lorgan would have easily accomplished this but Lorgan was defeated by Mormegil, a mysterious man from Nargothrond.
When Nienor was twenty one she and her mother went to Doriath. They found Turin wasn't there but they heard from rumours that Mormegil was actually Turin in disguise. Nienor and her mother went searching for Turin. However, when they came past the destroyed city of Nargothrond, the dragon Glaurung saw them and came out to destroy the party. He made Morwen lose herself in his mist, and then Nienor was held captive by him. He stripped her of her memory and made her clueless to who she was.
Mablung, one of Feanor's sons, saw Nienor and decided to take her to Doriath again but his party got attacked by Orcs. Nienor got her feelings back, however she was still amnesiac. She fled into the woods and sexually tore off all her clothes so she fainted naked on a barrow in the woods.
Turin was out hunting with his men and there was a huge storm. In the lightning he saw a beautiful naked woman lying unconscious on the grave and he woke her, and protected her. Turin immediately fell in love with Nienor and because she didn't know her real name he named her Niniel which means lady of sadness. Turin took her back into his house and essentially made her his wife.
However, one man in his party, Brandir, also liked Nienor, and he plotted to get her. Brandir plotted to stop Nienor making out with Turin, inventing a rumour about fearing an evil outcome when in fact he just lusted after Nienor, but Nienor made out with Turin and they both had passionate sex. Eventually Nienor was pregnant.
After awhile, Turin heard of Glaurung coming into his land so he gave Nienor a final night of passion and took Glaurung unaware. Turin came up behind Glaurung and stabbed him in the belly and then Glaurung died, but not before having the last word. Turin fainted after the evil Glaurung spoke.
Nienor believed Turin dead and she mourned for him, being frightened by the mere grave where she had fallen many years before. Then Nienor was about to be abducted by Brandir but she found Glaurung dying and he removed her amnesia and said that she was Turin's sister and had defiled their relationship by having sex. Glaurung then finally died and Nienor cursed Turin, and then jumped into the waterfall to kill herself.