The One Ring is essentially the central item that The Lord of the Rings revolves around. Everything relies on this one small piece of metal, and it has the power to affect not only those who come into possession of it, but also the world at large. It is the thing that Sauron is pursuing, and it's also the thing that the heroes need to keep safe until the time comes to destroy it in order to bring Sauron down and save the world from his evil. Frodo gaining possession of the One Ring is what sets off the adventure in The Lord of the Rings, and his uncle Bilbo's previous ownership of it was a large plot point in The Hobbit.
Clearly, this is something that is important to Middle-earth as a whole, as it has a massive effect on everyone. It can even bring those who possess it to a sort of madness, evidenced by the way that it affects Smeagol and turns him into the creature Gollum. It's also not the only powerful ring in existence, but its power and importance far outweighs that of the others. What is it about this specific Ring that makes it so significant? What are its magical properties, and why does Sauron want to get it back so badly?
How Was The One Ring Created?
While the One Ring was crafted by Sauron, he didn't just make a single ring and then call it a day. He had a much wider-reaching plan to extend his power over Middle-earth, which included the creation of a whole bunch of rings that he would put into the hands of powerful figures all over the world. There were 20 rings in all, divided among three of the races in Middle-earth: 3 for the Elves, 7 for the Dwarves, and 9 for Men. All of these rings were crafted with assistance from the Elves, but the One Ring, the final ring that Sauron had a hand in creating, was forged by him alone.
His end goal was to use the One Ring to unite the other rings and bring the most powerful beings in Middle-earth under his control. He knew that the One Ring would require an intense amount of power in order to accomplish this, so he concentrated a part of his soul within the Ring to imbue it with the power he would need. Unfortunately, this also bound his life force and fate to that of the Ring, which meant that if the Ring were to be destroyed, Sauron's power would be destroyed right along with it.
What Are The One Ring's Powers?
The primary function of the One Ring was to control the other Rings of Power, though it was never quite as effective as Sauron had hoped, as those who wielded the 3 Elven Rings never used them while Sauron had the One Ring, and the Dwarves who had rings were too mentally strong for Sauron to be able to crack. Much more useful to the wielder, one of the Ring's other powers was to augment the powers and abilities of the being that held it. People who were not naturally powerful to begin with might not be able to unlock the Ring's full power, as it would take Sauron or someone of a similar power level to be able to do something like that. However, it still had small effects on those who held it, for instance, Frodo could see for miles while in possession of the Ring, and Sam could hear much better.
One of the effects that is the most seen through The Lord of the Rings, and would be accessible to any mortal who held the Ring, was that it turned anyone who put the Ring on invisible. This is something that Bilbo and Frodo use on occasion, both intentionally and by accident. Of course, wielding the Ring came with a price as well, as it had a significant effect on those that possessed it. Gollum is an extreme example of this, but it's clear that the Ring had an effect on Frodo, as he became angrier and more withdrawn as his journey with the Ring went on, to the point where he didn't even want to throw the Ring into the fires of Mount Doom at the end. This kind of attachment to the Ring was also seen in Bilbo, who was just as reluctant to give the Ring up before he left the Shire. The Ring also affected those within its proximity, which is seen through Boromir and how the Ring affects his mind when he's around Frodo.