Which Tolkien character discovers the One Ring before Frodo inherits it?

Bilbo Baggins discovers the One Ring before Frodo inherits it.

In The Hobbit, Bilbo finds the Ring in the tunnels beneath the Misty Mountains after becoming separated from Thorin’s company. He encounters Gollum, wins a riddle contest, and uses the Ring’s power of invisibility to escape.

Years later, Bilbo gives the Ring to Frodo in the opening section of The Lord of the Rings. Gandalf eventually determines that Bilbo’s apparently ordinary ring is actually the One Ring created by Sauron.

Bilbo’s discovery is central to the connection between Tolkien’s two major Middle-earth novels. The Hobbit presents the Ring as a useful magical object, while The Lord of the Rings reveals its history, corrupting power, and importance to the fate of Middle-earth.