Nienna [niˈenna] is a fictional character in J. R. R. Tolkien's legendarium. She is introduced in The Silmarillion as one of the Ainur (angelic beings), one of the Queens of the Valar and one of the Aratar.
She was the sister of Mandos and Irmo. Her name meant She who weeps. She lived in the far West of Arda, grieved for the suffering of the world, and comforted the spirits of the dead who waited in the halls of Mandos:
Gandalf's rebuke of Frodo for wishing death upon Gollum in The Fellowship of the Ring is obliquely attributed in The Silmarillion to Gandalf's having been a disciple of Nienna in Valinor (Chapter 2, "Valaquenta"): "Wisest of the Maiar was Olórin [Gandalf]... [H]is ways took him often to the house of Nienna, and of her he learned pity and patience."
Nienna was the only Vala of female appearance who was not married, similarly to Ulmo among the male counterparts.
Nienna wept on the mound of Ezellohar, watering it with her tears. After the destruction of the Two Trees by Melkor, she wept on their remains, cleansing the filth of Ungoliant, and helping to nurture the fruit and the flower that became the Sun and the Moon. Nienna is considered one of the most powerful of the female Valar, alongside Varda and Yavanna. Although she represents Mercy, Compassion and Healing, her powers seem to include growth, as she was instrumental, together with Yavanna, in making the Two Trees, and healing their wounds from the poison of Ungoliant. She was also one of the few Valar who sided with the release of Melkor from his bondage after the Age of Peace, being compassionate of his suffering yet unaware, as Manwë was, of his unfailing evil.
In The Book of Lost Tales Nienna was named Fui or Qalmë-Tári and was married to Vefántur (Mandos), to whom she was not related in that context. She did not bring about the healing of the Two Trees and turned away Túrin and Nienor from her halls of Fui (named after herself).