What name does J.R.R. Tolkien give the ring forged by Sauron?

J.R.R. Tolkien calls Sauron’s forged weapon the One Ring.

The One Ring was created by Sauron in the fires of Mount Doom during the Second Age. He designed it to control the other Rings of Power and used much of his own power in its making. Its destruction is therefore essential to defeating him permanently.

The Ring passes through several important hands in the legendarium. Isildur cuts it from Sauron’s hand after the end of the Second Age, but loses it in the Gladden Fields. Déagol finds it there, and Sméagol kills him to take it. Bilbo later obtains it from Gollum, and Frodo carries it toward Mount Doom.

The One Ring is not one of the three Elven Rings, such as Narya or Vilya. It is also different from the Ring of Barahir, an heirloom associated with Aragorn’s family. Tolkien’s inscription is written in the Black Speech of Mordor using Tengwar letters.