The One Ring is the object Bilbo Baggins finds beneath the Misty Mountains in J.R.R. Tolkien’s The Hobbit.
Bilbo discovers the Ring in the underground tunnels after becoming separated from Thorin’s company. He encounters Gollum, wins a riddle contest, and uses the Ring’s power of invisibility to escape. The Hobbit presents the object mainly as a useful magical ring rather than fully explaining its history.
In The Lord of the Rings, Gandalf determines that Bilbo’s ring is actually the One Ring forged by Sauron. It contains much of Sauron’s power and can be destroyed only in the fires of Mount Doom, where it was made.
Sting is Bilbo’s sword, and the Arkenstone is the treasured jewel sought by Thorin. A palantír is a seeing-stone, not the object Bilbo finds in the caves.