Maiar

Sauron, a Maiar himself

Maiar are spirits that entered Arda to assist the Valar with shaping the world. Many Maiar were not named, but they were supposedly numerous. The Maiar had two leaders known as chiefs. The first chief was Eönwë, banner-bearer and herald of Manwë and Ilmarë, the handmaid of Varda.

History

Each Maia was associated with one or more Vala. The Maiar were less powerful than the Valar, but they did resemble them. The most powerful of Maiar were capable of opposing a Valar. At one occasion, the Maia Ungoliant managed to overcome Melkor by draining his power and trapping him into a cage, forcing him to scream for help from the Balrogs.

Characteristics

Similarly to the Valar, Maiar do not have a stable form.