Smaug is the dragon defeated by Bard in The Hobbit.
Smaug seized the Lonely Mountain and its treasure from the dwarves of Erebor before the events of the novel. When Bilbo enters the mountain, he discovers the dragon’s weakness: a bare patch in Smaug’s otherwise armored underside. Bilbo’s information helps Bard of Dale make the fatal shot.
Bard uses the Black Arrow, striking Smaug in the exposed area as the dragon attacks Lake-town. Smaug’s death is not the end of the conflict, because the treasure creates competing claims among dwarves, elves, and men. Tolkien’s other dragons, including Glaurung and Ancalagon, belong mainly to earlier legendary histories.