From The Lord of the Rings wiki
Smaug
Smaug the Golden was a powerful fire-drake of the Third Age who seized the Lonely Mountain and its vast hoard of treasure from the Dwarves of Erebor.
Smaug was a great dragon of Middle-earth, renowned for his immense size, impenetrable armour of scales, and devastating fire-breath. In the year 2770 of the Third Age, he descended upon the Lonely Mountain, destroying the kingdom of Dale and driving the Dwarves of Durin's Folk into exile. He claimed the entire wealth of the mountain for himself, sleeping atop the gold for nearly two centuries.
The Quest of Erebor
Smaug's presence remained a significant threat until he was confronted by Bilbo Baggins and a company of thirteen dwarves led by Thorin Oakenshield. During their infiltration of the mountain, Bilbo discovered a small patch of bare skin on the dragon's chest. This vulnerability proved fatal when the creature later attacked the nearby town of Esgaroth; he was struck down by Bard the Bowman, who used a black arrow to pierce the dragon's heart.
