"Námo, the elder [of the Fëanturi, masters of spirits] dwells in Mandos, which is westward in Valinor. He is the keeper of the Houses of the Dead, and the summoner of the spirits of the slain. He forgets nothing; and he knows all things that shall be, save only those that lie still in the freedom of Illúvatar. He is the Doomsman of the Valar; but he pronounces his dooms and his judgements only at the bidding of Manwë. Vairë the Weaver is his spouse, who weaves all things that have ever been in Time into her storied webs, and the halls of Mandos that ever widen as the ages pass are clothed with them.

- The Valaquenta, The Silmarillion by J.R.R Tolkien.

Race: Ainur
Division: Valar
Order: Fëanturi
Meaning: 'prison-fortress'
True Name: Námo
Titles: Doomsman of the Valar

(information from The Encyclopedia of Arda)