Know Your LotRO Lore: The One to rule them all

The One Ring could be considered the key to the domination of the others. Without it, the others had their own powers, but with it, Sauron would be able to control the ring-bearers and carry out his plans to have all kings of all nations in his hands. On this ring, Sauron inscribed the last two lines of the ancient rhyme lore of Black Speech written in tengwar script, only visible when the One Ring was made hot enough:

Ash nazg durbatulûk, ash nazg gimbatul,
ash nazg thrakatulûk, agh burzum-ishi krimpatul.

or

One Ring to rule them all, One Ring to find them,
One Ring to bring them all, and in the darkness bind them.

These were the words spoken by Sauron as he first wore the ring, and they are also the words heard by the Elves during this time, making them aware of Sauron's intentions.

The power of the One was similar to the Nine Rings, whereas a mortal bearer would appear invisible to other mortals. Unlike one of the Nine Rings though, this ring gave absolute power to the bearer, allowing them to dominate the will "of others in proportion to the native abilities of its wearer." This explains Frodo's temporary and sporadic dominion over Gollum, Sam's ability to understand the Orc speech in Mordor and Bilbo's ability to understand the speech of the Great Spiders in Mirkwood. It's important to note though, that if anyone of great power wore this ring, such as Galdalf, its power would quickly turn such greatness into the next Dark Lord.

At one point, Sauron attempted to enlist the aid of the Dwarves in finding this One Ring. He promised them the return of the three remaining Dwarven Rings and all of Moria for this one ring that he called "the least of rings" in an attempt at deceit. The Dwarves repeatedly refused Sauron's requests, which eventually brought Glóin and Gimli to Rivendell to meet with Elrond on the matter. This explains their presence during the Council of Elrond, and Gimli's involvement with the Fellowship.

This possession of the Ring has a very long and interesting history, but is very well documented in Tolkien's works. When it passes from Sauron's finger in the Battle of Dagorlad, it essentially changes hands seven more times (if you count Smeagol and Gollum separately) until it is ultimately destroyed in the Crack of Doom at Orodruin (Mount Doom).

The Ring's destruction immediately caused the death of Sauron, the destruction of Barad-dûr and of all Sauron's forces. This also caused the remaining rings to be powerless and worthless, except as relics or jewelry.