FAQ / What is Sauron
In the beginning there was Ilúvatar, the all-father, also called Eru, the One. The Ainur (sing. Ainu), the holy ones, spiritual angelic beings, were the offspring of his mind. In the "Music of the Ainur" the world was created and Arda, the earth, within it. Those of the Ainur who entered into the world and remained there are called the Valar (sing. Vala) and - of the same order, but of lesser degree - the Maiar (sing. Maia). The Maiar were the servants and helpers of the Valar.
Melkor was one of the Ainur who wanted to play his own tune in the "Music of the Ainur" and he also entered the world and destroyed many of the things the Valar had made. And he "corrupted" many of the Maiar who became his servants. Sauron, one of them, who later became the Dark Lord in Middle-earth, was originally a Maia, one of the servants of Aulë (a Vala). The Balrogs were also corrupted Maiar...