The ring that gives Bilbo invisibility in J.R.R. Tolkien’s The Hobbit is the One Ring. Bilbo finds it in the Goblin tunnels beneath the Misty Mountains after becoming separated from the dwarf company. He wins it from the creature Gollum by answering riddles and then uses its power to escape.
In The Hobbit, the ring initially appears to be a valuable magical tool that helps Bilbo survive. Its deeper identity becomes central in The Lord of the Rings, where Gandalf determines that it is the Ruling Ring forged by Sauron. The ring can make its wearer invisible to ordinary sight, but it also reveals the wearer to certain supernatural beings and exerts a corrupting influence.
Bilbo does not know the ring’s full history when he first takes it. This change in emphasis reflects Tolkien’s evolving conception of the object between the earlier children’s book and the later epic. The other named rings, including Nenya and Narya, are separate artifacts.