J.R.R. Tolkien’s The Hobbit centers on Smaug as its main enemy.
Smaug is a powerful dragon who occupies the Lonely Mountain after driving out the dwarves of Erebor. He guards the vast treasure hoard beneath the mountain, including the Arkenstone, and his presence is the central reason Thorin Oakenshield leads the quest involving Bilbo Baggins and the company of dwarves.
Bilbo enters the mountain and speaks with Smaug, using riddling and indirect language rather than immediately revealing his identity. During this encounter, Bilbo notices a bare patch in the dragon’s armored underside. That information is later passed to Bard of Dale, who uses the Black Arrow to kill Smaug.
Tolkien created other dragons, including Glaurung and Ancalagon the Black, but they belong primarily to the earlier history of Middle-earth found in The Silmarillion and related writings. Smaug is specifically the dragon of The Hobbit.