Rings of Power

The Rings of Power, including the One Ring, were created by Sauron to help him rule over Middle-Earth. Three were given to the Elves: Narya, which was originally given to Gil-Galad, then worn by Cirdan until he gave it to Gandalf; Vilya, which stayed with Gil-Galad until he gave it to Elrond; and Nenya, which went directly to Galadriel. Seven went to the Dwarf Lords, and were all taken back by Sauron or dragons by the Third Age. The last nine went to mortal Men, who eventually became the Nazgul (Ringwraiths).

That makes twenty Rings. Mary Sues often create a twenty-first ring in order to seem speshul.

More about the Rings of Power at The One Wiki To Rule Them All