Which 1937 book by J.R.R. Tolkien introduced Bilbo Baggins?

J.R.R. Tolkien introduced Bilbo Baggins in The Hobbit, published in 1937.

The book follows Bilbo’s unexpected journey with the wizard Gandalf and a company of dwarves led by Thorin Oakenshield. Their expedition aims to reclaim the Lonely Mountain and its treasure from the dragon Smaug. Tolkien originally wrote the story for his children, and its success led his publisher to request a sequel.

That sequel became The Lord of the Rings, which grew into a much longer and darker work. The Hobbit is often described as a children’s fantasy, but it also contains early versions of ideas that Tolkien later expanded, including the significance of the ring Bilbo finds in the goblin tunnels. The 1937 text was later revised in part to better fit the sequel’s developing mythology.