Smaug was considered to be the last fire dragon to exist in Middle-earth in the Third Age. He came from the mountains in the north fascinated by the riches of dwarves which included gold, gemstones and famed Arkenstone. During one of his attacks he devastated both dwarven city of Erebor and the neighboring human city of Dale. In that time he killed any dwarves or men who tried to stop the massacre, only King Thrór along with few dwarves managed to escape the mountain through a secret door. Powerful Smaug ruled the Lonely Mountain for two centuries unchallenged and the lands around it became known as the Desolation of Smaug. Inside the mountain the dragon spent all his days lying at the top of his great treasure.
My armour is like tenfold shields, my teeth are swords, my claws spears, the shock of my tail is a thunderbolt, my wings a hurricane, and my breath death!
~Smaug
However after almost two hundred years a small company of fourteen adventurers consisting of twelve dwarves, the hobbit Bilbo Baggins and the great wizard Gandalf set on a journey to reclaim once lost Erebor. They traveled through lands of Middle Earth and entered Smaug’s mountain lair using a secret door. The group decided to send Bilbo to the treasure chamber alone as he was a company’s “burglar”. His job was to gather information using stealth and then steal everything he could without waking Smaug. Unfortunately the dragon noticed Bilbo and amused by a hobbit he conversed with him. The beast wanted to deduce his origin and purpose and immidiately surmised that he was helping Thorin, the company’s leader and that the rest is waiting for a special gem, the Arkenstone.
After that furious Smaug left the mountain and flew loosening his flame upon the land with the intention to raze the Lake-town. In the city brave Bard the Bowman, heir to the throne of Dale managed to rally townsmen to defend the city. Arrows of bowmen did not harm the dragon’s armour at all but thanks to information about a vulnerability on Smaug’s skin gained from Biblo, Bard knew what to do. He fired a powerful black arrow into a weak point on the dragon’s belly. That shot penetrated the his thick skin and did a lot of damage which caused the dragon to roar in fury and pain. Smaug fell from the sky into the ruins of Dale and died, that was the end of dragons in whole Middle Earth.
Source: https://lotr.fandom.com/wiki/Smaug