Bilbo Baggins finds the One Ring in the opening history of The Lord of the Rings.
Bilbo discovers the Ring in the tunnels beneath the Misty Mountains during the events of The Hobbit. He encounters Gollum there, wins a riddle contest, and uses the mysterious ring’s power of invisibility to escape. At the time, neither Bilbo nor the reader fully understands the object’s identity or danger.
Years later, Bilbo gives the Ring to his cousin and heir, Frodo Baggins, in the Shire. Gandalf eventually determines that it is the One Ring forged by Sauron, transforming Bilbo’s earlier adventure into the beginning of a much larger crisis. This connection makes The Hobbit a direct narrative predecessor to The Lord of the Rings.
Gollum is a common wrong answer because he possessed the Ring for centuries before Bilbo found it. Frodo is another common mix-up because he carries it through most of the later story. The first major character in the published narrative to find it is Bilbo.