Maiar

Warning: Wikipedia contains spoilers

The Maiar are those spirits which descended to Arda to help the Valar to shape the World. Singular is Maia.

Each of the Maiar was associated with a particular Vala. For example, Ossë, as a spirit of the sea, belonged to Ulmo, while Curumo, who came to be known in Middle-earth as Saruman, belonged to Aulë the Smith. Others included Sauron (originally also of Aulë's people), and Olórin, known as Gandalf, who belonged to Manwë and Varda.