The Maiar (singular: Maia) are a fictional class of beings from J. R. R. Tolkien's high fantasy legendarium. Supernatural and angelic, they are "lesser Ainur" who entered the cosmos of Eä in the beginning of time. The name Maiar is in the Quenya tongue (one of several languages constructed by Tolkien) from the Elvish root maya- "excellent, admirable".
Commentators have noted that since the Maiar are immortals but can choose to incarnate fully in Men's bodies on Middle-earth, they can be killed; Tolkien did not explain what happened to them then. Others have observed that their semi-divine nature and the fact that they can be sent on missions to work out the divine purpose makes them much like the angels of Christianity.
Tolkien stated that "Maia is the name of the Kin of the Valar, but especially of those of lesser power than the 9 great rulers".
In the Valaquenta, Tolkien wrote that the Maiar are "spirits whose being also began before the world, of the same order as the Valar but of less degree". According to the Valaquenta, many Maiar associated themselves with a particular Vala; for example, Salmar created for his lord Ulmo great conches who produce the music of the sea known as Ulumúri, while Curumo, who came to be known in Middle-earth as Saruman, was with Aulë the smith. The being once known as Mairon also was with Aulë, before being corrupted by Melkor and becoming Sauron, the main antagonist of The Lord of the Rings. Sauron continued his association with smithcraft by befriending the Elven-smiths of Eregion during the Second Age, so that he could gain power over the other rings by forging his One Ring. On the other hand, certain Maiar like Olórin and Melian develop associations with multiple Valar Lords and Queens.
Being of divine origin and possessing great power, the Maiar can wander the world unseen or shape themselves in fashion of Elves or other creatures; these "veils", called fanar in Quenya, could be destroyed, but their true-being could not.