We cannot use the Ruling Ring. That we now know too well. It belongs to Sauron and was made by him alone, and is altogether evil. Its strength, Boromir, is too great for anyone to wield at will, save only those who have already a great power of their own. But for them it holds an even deadlier peril. The very desire of it corrupts the heart.
— Elrond, The Fellowship of the Ring