Sauron is the Tolkien character known as the Lord of the Rings. The title refers to Sauron’s role as the maker and master of the One Ring, through which he sought power over the other Rings of Power.
Sauron was originally a powerful spirit called a Maia who served the first Dark Lord, Morgoth. After Morgoth’s defeat, Sauron became the principal enemy of the Second and Third Ages. He helped create the Rings of Power and secretly forged the One Ring in Mount Doom.
The title does not mean that Sauron physically owns every ring at all times. It identifies his intended dominion over the ring bearers and the power embodied in the rings. The Lord of the Rings is also the title of Tolkien’s epic novel.
Sauron’s body and power changed across the ages, but his central ambition remained control over Middle-earth. His defeat depends on destroying the One Ring rather than simply defeating him in battle.