Sauron forged the One Ring in the fires of Mount Doom in J.R.R. Tolkien’s legendarium.
He created it during the Second Age to dominate the other Rings of Power and extend his control over their wearers. Sauron secretly placed a large portion of his own power into the Ring, which made it exceptionally potent but also tied his survival to its existence. The Ring’s inscription is written in the Black Speech of Mordor.
Celebrimbor and the Elven-smiths of Eregion forged the other Rings of Power, but Sauron forged the One Ring alone. This distinction causes a common mix-up: Celebrimbor was responsible for the Three Rings of the Elves, while Sauron created the ruling Ring. Isildur cut it from Sauron’s hand after the fall of Barad-dûr, but he did not destroy it, allowing its history to continue into The Hobbit and The Lord of the Rings.