The One Ring is the fictional object that gives its bearer invisibility in J.R.R. Tolkien’s The Lord of the Rings.
Sauron forged the One Ring in the fires of Mount Doom to control the other Rings of Power and dominate their bearers. When an ordinary person puts it on, the wearer becomes invisible to normal sight, although the Ring also draws the wearer toward Sauron’s power.
The Ring is not merely a magical cloak. It contains much of Sauron’s power, which is why destroying it is necessary to defeat him permanently. Its influence also affects characters who never wear it, including those who desire or attempt to protect it.
Bilbo finds the Ring before the events of The Lord of the Rings, and Frodo inherits it from him. Frodo carries it toward Mordor while Samwise Gamgee helps him complete the journey.