Sauron (Earth-4552)

Sauron (or Þauron; Quenya; IPA: [ˈsaʊron] or Vanyarin [ˈθaʊron] - "Abhorred"), the eponymous Lord of the Rings, was a fallen Maia, the creator of the One Ring, and the most trusted lieutenant of his master Morgoth (Melkor, the first Dark Lord). After Morgoth's defeat in the First Age, Sauron became the second Dark Lord and strove to conquer Arda, creating the Rings of Power for this purpose. In the Second Age, he was defeated in the War of the Last Alliance by the last line of defense: Elves and Men.

During the battle, Isildur managed to cut off Sauron's finger with the ring on it, causing the destruction of his corporeal form and scattering his armies. After spending hundreds of years lying dormant and slowly regaining his strength, Sauron returned to power in the Third Age, but was finally defeated in the War of the Ring through the destruction of the One Ring.

Origin
Sauron was originally a Maia of Aulë the Smith named Mairon, meaning "admirable", and learned much from him in the ways of forging and crafting, becoming a great craftsman, and mighty in the lore of Aulë's people. Although he was a Maia spirit, and not as mighty as the Valar, Mairon was one of the most powerful Maiar, being far stronger than others such as Olorin and Curumo (who was also a servant of Aulë).

Serving Morgoth
During this time, Mairon was as Eru had created him: good and uncorrupt. His greatest virtue was his love of order and perfection, disliking anything wasteful. However, this would also prove to be the source of his fall, for in the Dark Lord Morgoth, Mairon saw the will and power that would help him achieve his own goals and desires faster than if he had pursed them on his own. So great was his allegiance that even in later days, after Morgoth was defeated and locked outside the confines of the world, Sauron encouraged and coerced some Men to worship Morgoth as the one and true god. However, while Morgoth wanted to either control or destroy the very matter of Arda itself, Mairon's desire was to dominate the minds and wills of its creatures.