What is the history of Sauron?

In J.R.R. Tolkien's Middle-earth legendarium, Sauron is a powerful and malevolent being, who played a major role in the events leading up to and during the events of The Lord of the Rings. Once a servant of the dark lord Morgoth, Sauron first appeared in Tolkien's novel The Silmarillion, where he forged the One Ring, an artifact of immense power that he used to rule over Middle-earth.

Over the course of the Second and Third Ages of Middle-earth, Sauron amassed an army and waged war against the peoples of Middle-earth, seeking to conquer and enslave them. He was eventually defeated by an alliance of Men and Elves, led by the heroic figure Isildur, who cut the Ring from Sauron's finger, causing him to lose much of his power.

Despite his defeat, Sauron's spirit endured, and he gradually began to regain strength, eventually returning to Middle-earth in the form of a dark lord once again. The events of The Lord of the Rings follow the quest of Frodo Baggins to destroy the Ring and defeat Sauron once and for all, in a final battle for the fate of Middle-earth.