Ainur

According to the Ainulindalë within Tolkien's cosmology, Eru Ilúvatar first conceived the Ainur, immortal spirits 'made of the thought of Eru'. The Ainur responded to themes introduced by Ilúvatar by singing the Music of the Ainur; when Ilúvatar gave being to that music it brought Eä, the created universe, into existence and shaped Arda. Some Ainur who 'felt concern for the Creation' entered Eä to take part in its governance and care; these entrants are named in the narratives as the Valar (the greater Powers) and the Maiar (the lesser Powers).

As described in the sources, the Ainur are fundamentally spirits and thus lack a single, consistent physical form prior to entering the world. The accounts emphasize their immaterial, 'immortal' nature rather than detailed bodily description. When Ainur enter the created world they may assume forms appropriate to their office: the Valar and Maiar are represented in the stories by figures such as Manwë, Melkor/Morgoth and Tulkas among the Valar, and Gandalf, Sauron and the Balrogs among the Maiar, but the supplied material stresses there is no uniform physical template for all Ainur and that their primary mode is spiritual rather than corporal.

The Ainur's defining activity is their participatory creativity: the Music of the Ainur shaped the fabric of reality and, when given being by Eru, became the universe. Those Ainur who entered Eä serve as guardians and shapers of Arda, exercising providential influence, governance, and craftsmanship. They possess genuine moral agency and free will and so are capable of goodness or of rebellion and corruption (the chief example being Melkor/Morgoth). Valar and Maiar are powerful but limited: they can influence the course of events and pattern fortune or providence without wholly negating the free choices of Elves and Men. Although fundamentally immortal spirits, many Ainur may assume embodied forms; in such incarnations Maiar in particular can be slain in bodily form (examples in the narratives include Gandalf and Balrogs), while sources note the ultimate fate of a slain Maia is left unclear in the supplied materials.