Which Tolkien novel features the dragon Smaug as its main dragon?

The Hobbit features the dragon Smaug as its central dragon.

Smaug occupies the Lonely Mountain, also called Erebor, after driving the dwarves from their kingdom. He guards the treasure accumulated by the dwarves and becomes the main obstacle in the latter part of Bilbo Baggins’s adventure. Bilbo first encounters him while secretly exploring the mountain and discovers a vulnerable area in the dragon’s armour.

The character of Smaug combines the traditional European dragon image with Tolkien’s interest in language and personality. He is intelligent, vain, suspicious, and capable of conversation. His dialogue with Bilbo is as important to the scene as the danger of his fire.

The Hobbit was published in 1937 as a standalone children’s fantasy. The Lord of the Rings later expanded the world and referred back to events involving Smaug, but Smaug does not appear as an active character in that trilogy. The Silmarillion describes earlier dragons, including Glaurung, which is why readers sometimes confuse Tolkien’s different dragon stories.