Smaug is the dragon who takes Erebor in J.R.R. Tolkien’s The Hobbit.
Smaug attacks the Dwarf kingdom beneath the Lonely Mountain, also called Erebor, and drives its inhabitants into exile. He takes the immense treasure hoard for himself and sleeps among it for many years. Thorin Oakenshield later leads a company of Dwarves to reclaim the mountain, with Bilbo Baggins accompanying them.
Bilbo enters Smaug’s lair and speaks with him, using riddling language and the name “Barrel-rider” to conceal his identity. During the conversation, Bilbo notices a bare patch in the dragon’s armor-like underside. That information allows Bard the Bowman to strike Smaug with the Black Arrow.
Smaug is distinct from Tolkien’s other dragons. Glaurung appears in the First Age story of Túrin Turambar, Ancalagon is a great dragon of the War of Wrath, and Scatha is a dragon of the Grey Mountains. Those names belong to different stories and eras.