Sauron's race is Maia.
Among those of his servants that have names the greatest was that spirit whom the Eldar called Sauron, or Gorthaur the Cruel. In his beginning he was of the Maiar of Aulë, and he remained mighty in the lore of that people. In all the deeds of Melkor the Morgoth upon Arda, in his vast works and in the deceits of his cunning, Sauron had a part...
-- Ainulindalë - Of the Enemies
Sauron was originally Melkor's lieutenant, and a lesser being:
And Melkor made also a fortress and armoury not far from the north-western shores of the sea, to resist any assault that might come from Aman. That stronghold was commanded by Sauron, lieutenant of Melkor...
-- Quenta Silmarillion - Chapter 3 - Of the Coming of the Elves and the Captivity of Melkor
The Maiar are lesser Ainur:
With the Valar came other spirits whose being also began before the World, of the same order as the Valar but of less degree. These are the Maiar, the people of the Valar, and their servants and helpers.
-- Ainulindalë - Of the Maiar
Sauron created the One Ring himself, in order to gain control over the wearers of all the other rings.
Now the Elves made many rings; but secretly Sauron made One Ring to rule all the others...
Because he put so much of his own power into the Ring, its destruction was essential to defeating him:
And much of the strength and will of Sauron passed into that One Ring; for the power of the Elven-rings was very great, and that which should govern them must be a thing of surpassing potency...