Nienna (‘she who weeps’) is the Lady of Pity and Mourning. She is one of the Valar and the sister to Mandos (Námo) and Lórien (Irmo), in addition to being among the Aratar, the eight most powerful Valar.

When the Music of the Ainur was put forth to create Middle-earth, Nienna sang of grief and suffering. Because of this, the sound of mourning and sorrow entered into the design of Middle-earth. She sings often of the wounds that Arda has suffered throughout its creation.

Nienna has no spouse and dwells alone on the borders of the world, coming often to the halls of Mandos, the Houses of the Dead, where all the spirits of the slain dwell. She brings strength to these lost spirits and wisdom to replace their sorrow. The wisest of the Maiar, Olórin, came often to the house of Nienna where she taught him pity and patience.

Nienna also helped to create the Two Trees of Valinor by watering, with her tears, the mound upon which the trees were grown. After Melkor used Ungoliant to destroy the trees, Nienna once again wept on the mound in order to remove the stains that Ungoliant had left there, and allowing the trees to bear their last fruits. However, when Melkor was brought before Manwë to beg forgiveness for his actions, Nienna was the only Valar to speak on his part.
Encyclopedia entry originally written by Ringhilwen