The dragon in J.R.R. Tolkien’s 1937 novel The Hobbit is Smaug.
Smaug occupies the Lonely Mountain, also called Erebor, after driving out the Dwarves of the kingdom under the mountain. Thorin Oakenshield leads a company to reclaim their homeland and its treasure, with Bilbo Baggins serving as the burglar chosen for the expedition.
Bilbo discovers a weak spot in Smaug’s armor and later communicates this information to the people of Lake-town. The dragon attacks Lake-town but is ultimately killed by Bard the Bowman, who uses the Black Arrow. Smaug’s death helps trigger the Battle of the Five Armies.
Glaurung and Ancalagon are dragons from Tolkien’s First Age stories, while Scatha is another dragon associated with the Grey Mountains. They are not alternative names for Smaug and belong to different episodes of Tolkien’s mythology.