:The Lord of the Rings
Sauron, whose name means "the abhorred", was a Maia serving the evil Vala known as Melkor, the Enemy. When Melkor ruled his dark kingdom of Utumno, he set Sauron to rule his armory in Angband. Sauron remained his general, taking care of business, even after the War of Powers at the end of the First Age of Stars, when Melkor (by then called Morgoth) was chained. After Melkor's final defeat and the destruction of Angband, Sauron remained, becoming the chief architect of evil in Middle-earth.
In the Second Age of the Sun, Sauron made himself a fair and noble shape and took the name Annatar, "giver of gifts". He tricked the Elves of Eregion into making the nineteen rings of power, in an attempt to gain control of the Elves. In the fires of Mount Doom, he secretly forged the One Ring, putting much of his strength and willpower into it in order to make it strong enough to control the other, very powerful, rings. However, as soon as Sauron put the One Ring on his finger, the elves became aware of his intentions. They managed to hide the three most powerful rings - Narya, Nenya and Vilya - from Sauron, and they were unspoiled and kept in great secrecy by the Eldar. The sixteen other rings, Sauron took and gave instead to the dwarves and humans, the mortal races being more susceptible to his corruption.
Sauron then made war on the Elves of Middle-Earth, driving them far west into the mountains. The Men of Númenór came to the aid of the Elves, leaving their island-kingdom with a great army. Sauron was driven out of the West, and bided his time in Mordor, his new dark kingdom. However, made proud by their power, the Númenóreans once again came to Middle-Earth to defeat Sauron and proclaim themselves lords of the land as well as the seas. As Sauron realized he had no chance against them in battle, he came out of Mordor and surrendered.
The Dark Lord was brought to Númenór as prisoner of the king Ar-Pharazôn. There Sauron obtained the ear of the king, and corrupted his people to build temples and sacrifice to Morgoth, the dark enemy of the World. Sauron led the Númenóreans to attack the Valar and Elves of the Undying Lands. As their fleet landed in the realms that were forbidden to mortals, they drew upon themselves a great cataclysm. The entire Númenorean host was destroyed as the mountains came down upon them. The island of Númenórë sank beneath the sea, and the once-proud kingdom was lost in the waves. Thus Sauron caused the Change of the World, and his first shape was destroyed.
However, his spirit fled to Mordor, and there he took a new form. This second body of Sauron was that of a great warrior, with burning black skin, clad in black armor. At the end of the Second Age, his power grew once more, and the Men and Elves of Middle-Earth formed the Last Alliance and made war on him. As can be seen in the introduction to the film, the One Ring was cut from Sauron's finger by Isildur, prince of the descendants of Númenór. With the source of his power lost, Sauron was again destroyed. What happened to the Ring after this can be found out in Lord of the Rings.
So great was Sauron's power that he once more made himself a form, in the Third Age of the Sun. He manifested himself in a great disembodied Eye which never blinked, ringed with flames and darkness. He started searching for the Ring once again, because he still needed it to fulfill his plans on world mastery. At this time, Sauron bred the creatures of the Uruk-Hai and Olog-Hai. In the War of the Ring, Sauron's spirit was finally banished from the World through the destruction of the One Ring.
Should you notice any inaccuracies in this text, please Blab! me. There is more to say about Sauron, but this will have to do for a short biography. Everything does not fit in one node.