"Three Rings for the Elven-kings under the sky, seven for the Dwarf-lords in their halls of stone, nine for Mortal Men doomed to die, one for the Dark Lord on his dark throne in the Land of Mordor where the Shadows lie". These iconic lines from Lord of the Rings explain that the One Ring that the story centers around is not the only Ring of great importance in the world of Middle-Earth. There may be One Ring to rule them all, but the other Rings of Power have their roles as well.
But what exactly are those roles? The other Rings of Power and their owners are barely touched on in the story, but if the One Ring was that powerful, the others that Sauron created must carry their own power as well, right? Why were these Rings created and given out across the lands of Middle-Earth, and what exactly do all of them do?
There were 20 Rings in total, all of them forged in the Second Age. Sauron had a hand in creating all of them (though he did not physically make every Ring), in an effort to turn the various leaders of different races and kingdoms across Middle-Earth to his side of evil. The idea was to create a master Ring that could control all of the others (this eventually became the One Ring), and he would give the other Rings to powerful people across the Earth. He especially wanted to find a way to rule over the Elves, because he was at war with them and any other attempt to defeat them would have required a massive military. This is where the first of the Rings comes in.
Three Rings For The Elven-Kings
The first Rings to be made were the Elven rings, forged by Celebrimbor. Sauron came to Celebrimbor in the form of "Annatar", an emissary of the Valar, and gave the Elves the knowledge required to form the Rings. He told them that by forging these Rings, they would be given new powers and would be able to transform Middle-Earth. The Elves formed some lesser rings at first, but eventually, Celebrimbor created the Three Rings with the knowledge that "Annatar" had given him.
The Three Elven Rings were Narya (the Ring of Fire), Nenya (the Ring of Water), and Vilya (the Ring of Air). Narya was first worn by Gil-galad (who was King of the High Elves), and it eventually made its way into the possession of Gandalf. Gil-galad also owned Vilya, and when he died, Elrond inherited it. Nenya was owned by Galadriel, and she was the only person to ever own it. Rather than making their owner invisible, these Rings themselves were invisible.
As for the specific powers of the individual Rings, Narya is described as having the power to inspire hope in those who were around the wielder, and also gives the owner resistance to the "weariness of time". Nenya possessed the ability to preserve and protect from evil, and it is said that Galadriel used these powers to create and protect Lothlórien, though it also increased her longing to go to the Undying Lands. Vilya was the greatest of the Three Elven Rings. Its specific powers are never stated, but it has been inferred that it also has a healing and preserving power like Nenya. There is also speculation that it had the power to control minor elements and see into the future, but it's unclear if these were effects of the Vilya or just the natural abilities of Elrond, who was the owner. All of these Rings were worn by their owners until they departed from the Grey Havens at the end of the Third Age.
Seven For The Dwarf-Lords
The Dwarves possessed seven Rings, six of which were given to them by Sauron, the seventh being a gift to Durin III by Celebrimbor (though it was still created by Sauron). The Dwarves used their Rings to build their famed hoards of treasure, and Sauron was never able to get the Dwarf-lords who bore the Rings to submit to his will. These Rings also did not turn the bearers invisible, and the natural strength and hardiness of the Dwarves made them resistant to the adverse effects the Rings were supposed to have (including Sauron's control). Four Rings were destroyed by dragon fire, and three more were taken back by Sauron. The last Ring to leave the possession of the Dwarves (the one originally owned by Durin III) was lost when Durin's descendant Thráin II was captured and tortured by the Necromancer (who was Sauron in disguise).
Nine Rings For Mortal Men
The nine remaining Rings were given to evil-hearted Men who were doomed to become the Ringwraiths, controlled by Sauron. The Nine Rings given to these Men gave them a great amount of wealth and power, and allowed them to become powerful Sorcerers. However, after a long time of bearing these Rings, they started to see phantoms and delusions brought on by Sauron, and were corrupted and lost any ability to resist evil. They fell under Sauron's control permanently, and their actions and strength were directly linked to him, making them little more than extensions of his will. There is no mention of the Nine Rings when the Nazgûl appear, which implies that they no longer need to wear the Rings to be under Sauron's control.
The One Ring
The final Ring was the One Ring, which was forged by Sauron himself and powerful enough to control the other nineteen Rings. His original plan was to create this Ring in order to rule over the Elves who were in possession of their own Great Rings, without any need for military interference. In the end, the plan didn't go as imagined and the One Ring was unable to have full control over the other Rings, but Sauron's own power was increased while he wore the Ring, and gave him military might that he otherwise would not have gained.
The fate of this Ring, of course, is the most well-known of all of them, passing from Sauron to Isildur after his initial defeat, then to Sméagol, Bilbo, and finally to Frodo. Despite his efforts in forging a whole host of Rings, Sauron's ultimate attempt at power led to his final downfall at the hands of Frodo Baggins when the One Ring was finally cast into the fires of Mount Doom.