Sauron was originally a
Maia to Aule. (A
maia is a lesser god who is subservient to the greater ones)
He eventually went to the service of Morgoth, and became his lieutenant.
Sauron returned and entered Mordor and erected the tower of Barad-Dur. When the Numenoreans challenged him, he went as a prisoner, and eventually became a trusted advisor. The Numenoreans tried to fight the greater gods and they all died.
Once he came back, he slipped back to his old ways. He aided the Elves in making rings of power, and eventually he made the One
Ring, or the Ruling
Ring.
Later on, Sauron gave some of the rings of power to men, and eventually they fell under the power of the
Ring and became the Nazgul.
The words on the
ring are: One
ring to bring them all and in the
darkness bind them.
The elves and men formed the "last alliance" and went to fight the hosts of Mordor. They laid siege to Mordor. Then Sauron came and killed quite a few elves and men before killing Gil-Galad and Elendil before Isildur
cut the Ring from his
finger. Barad-Dur was leveled to the ground, but its foundation was not destroyed, because its power was tied with the ruling Ring.
Sauron hid in Mirkwood, and the wizards came from over the sea to challenge Sauron's power. (The wizards are also lesser gods) Sauron eventually went back to Mordor and rebuilt Barad-Dur.
Eventually,
Frodo and Sam threw the Ring into Orodruin, or Mount Doom, and the Ring was destroyed and the power of Sauron was diminished forever.
