Smaug is the dragon in The Hobbit who guards the treasure beneath the Lonely Mountain.
Tolkien presents Smaug as an intelligent, articulate, and highly self-confident dragon rather than merely a destructive beast. He has occupied Erebor since driving out the Dwarves of the Kingdom under the Mountain.
Bilbo Baggins enters the treasure hall and speaks with Smaug while trying to discover a weakness. Bilbo notices a bare patch in the dragon’s armor-like underside and later reports it to the people resisting Smaug.
The dragon’s death leads directly to the Battle of the Five Armies, because control of the hoard becomes a source of conflict among Dwarves, Men, and Elves. Smaug is distinct from Tolkien’s earlier dragon Glaurung, who appears in the legends later published in The Silmarillion.