The dragon in J. R. R. Tolkien’s The Hobbit is Smaug.
Smaug is the main antagonist of Tolkien’s 1937 novel. He invaded the Dwarves’ kingdom beneath the Lonely Mountain, or Erebor, drove them into exile, and claimed their vast treasure hoard. Bilbo Baggins joins Thorin Oakenshield and twelve other Dwarves on a quest to reclaim the mountain, with help from Gandalf.
Smaug is not merely a monstrous animal: he is intelligent, articulate, vain, suspicious, and skilled at manipulating conversation. Bilbo’s exchange with him is one of the novel’s central scenes. During their encounter, Bilbo notices a vulnerable patch in the dragon’s armor-like underside, information that later helps lead to Smaug’s downfall.
Tolkien drew on older dragon traditions, especially the dragon in the Old English poem Beowulf and the Norse legend of Fáfnir. The other options are dragons from Tolkien’s wider mythology: Scatha belongs to the history of the Grey Mountains, Ancalagon appears in The Silmarillion, and Glaurung is from the First Age.