Smaug the Dragon is the main antagonist of 1937 classic novel The Hobbit by J. R. R. Tolkien and it's Peter Jackson films 2012-2014. He will also appear in a The Hobbit: There and Back Again set in 2014.
Smaug was a dragon in the Third Age. One of the last of his kind, Smaug demolished Dale, and captured Erebor, the Lonely Mountain, from the Dwarves. For about two hundred years, Smaug hoarded Erebor's treasures before a company of dwarves led by Prince Thorin Oakenshield made their way back to the mountain along with Hobbit Bilbo Baggins. Bilbo entered to find and retrieve the arkenstone and bring to Thorin. The wizard Gandalf the Grey had departed from the company and left for Dol Guldur. Bilbo snuck into the treasure hoard but Smaug awakened and eventually found him.
After a discussion, Smaug revealed that he was aware of Bilbo's intentions and attempted to kill him, but Bilbo used the One Ring to hide again and managed to escape. Smaug found Thorin and the dwarves and they battled fiercely until Smaug realized that the dwarves were being aided by the Lake-men of Lake-Town. Smaug was distracted by Thorin, who unveiled a large golden statue that they had forged during the battle. They used the gold to distract Smaug due to his greed of gold long enough for the statue to melt into golden pools that they used to try and drown Smaug in it.
This strategy failed as Smaug burst out of the streams of gold, shook off all the gold and flew into the sky, heading for Lake-Town, intending to destroy it. As Bilbo remains horrified at the result in their quest, Smaug quoted "I am fire! I am...death!"
- Smaug along with the Necromancer/Sauron are both played by Benedict Cumberbatch in The Hobbit films.