What is the name of the ring in J.R.R. Tolkien's 'The Lord of the Rings'?

The name of the ring in J.R.R. Tolkien's The Lord of the Rings is the One Ring.

Sauron created the One Ring in the fires of Mount Doom during the Second Age, secretly placing much of his power into it. Its purpose was to control the other Rings of Power and dominate their bearers. The famous inscription, written in the Black Speech of Mordor, begins: “One Ring to rule them all.”

The Ring first appeared in The Hobbit (1937), where it mainly functioned as a magical invisibility ring. Tolkien later revised parts of that story so the Ring would fit its much darker role in The Lord of the Rings (1954–55). It is also called the Ruling Ring, Isildur's Bane, and the Precious, but these are alternative titles rather than the standard answer to the question.

Bilbo Baggins found it, Frodo Baggins carried it toward Mordor, and its destruction ultimately ended Sauron's power.