The dragon faced by Bilbo in J.R.R. Tolkien’s The Hobbit is Smaug.
Smaug occupies the Lonely Mountain and has taken the treasure of the dwarf kingdom of Erebor. Thorin Oakenshield leads a company of dwarves to reclaim the mountain, while Bilbo enters the dragon’s lair as the group’s burglar. Bilbo’s conversation with Smaug is one of the book’s central scenes.
Smaug is portrayed as intelligent, proud, suspicious, and highly skilled with words. During their exchange, Bilbo avoids giving his real name and uses riddling descriptions instead. He notices a vulnerable patch in the dragon’s armor-like underside, information that later reaches the archer Bard.
Smaug is sometimes confused with Tolkien’s other dragons. Glaurung appears in The Silmarillion’s First Age stories, Ancalagon the Black belongs to the War of Wrath, and Scatha is a separate dragon associated with the Grey Mountains. Smaug is specifically the dragon of The Hobbit.