Smaug, great fire drake of the North, for a time, King Under the Mountain

Prompt credit goes to Doomflower @Shooflower

"Smaug was a fire-drake of the Third Age, considered to be the last "great" dragon of Middle-earth. He was drawn to the enormous wealth amassed by the Dwarves of the Lonely Mountain during King Thrór's reign. He laid waste to the nearby city of Dale and captured the Lonely Mountain, driving the surviving Dwarves into exile.

For 171 years, Smaug hoarded the Lonely Mountain's treasures to himself, staying within the mountain, until a company of Dwarves managed to enter the Lonely Mountain and awaken him from hibernation. Correctly believing that the Dwarves had received assistance from the men of Lake-town in entering the Lonely Mountain, Smaug left the mountain to wreak destruction upon Lake-town, nearly destroying it before being slain by Bard the Bowman."