Use this tag when asking about the primary antagonist of J. R. R. Tolkien's The Lord of the Rings, not just for questions with 'Sauron' in them. Should also be used in conjunction with the [tolkiens-legendarium] tag. Also tag with [the-lord-of-the-rings] where appropriate.
Sauron is, in essence, a fallen angel ("Maiar") in the pantheon Tolkien created for the Lord of the Rings. In the Third Age (the time in which the Lord of the Rings is set) he directly controls the land of Mordor and indirectly controls and influences large swathes of Middle Earth. He is the creator of the One Ring which plays a major role in both the Hobbit and the Lord of the Rings.
This tag should be used when referring to the powerful being created in the lore of Middle-Earth. Try to avoid including this tag if your question merely mentions or features Sauron. Should also be used in conjunction with tolkiens-legendarium.