Smaug the Mighty
The first certain date in the history of Smaug is the year 2770 of the Third Age, when he came to the Lonely Mountain destroying the Dwarf-kingdom as well as the nearby township of Dale. The origins of this great fire-drake are unknown but it is presumable that he was bred in Angband in the late First Age. Smaug was not only strong and terrifying in his wrath, he could also be very cunning and understood and spoke the Common Speech. He was red-golden and covered in hard scales except for his soft belly which he had encrusted with gems. He had gathered all the treasures of the Dwarves into a huge pile in a great hall under the Mountain, and there he slept. Smaug's arrogance was finally his downfall, for in showing off his gem-armour to the hobbit Bilbo Baggins he had also displayed an open place in it. A thrush had overheard Bilbo speaking of it, and he flew to Bard of Dale and told him how to kill the dragon. And so it was that in the year 2941 of the Third Age the last fire-drake and the greatest dragon of his time, Lord Smaug the Impenetrable, was killed with the Black Arrow and rests now in the shallow waters of the Long Lake.
The name Smaug has an amusing background, here's what Tolkien wrote about it in 1938:
"The dragon bears as a name - a pseudonym - the past tense of the primitive Germanic verb Smugan, to squeeze through a hole: a low philological jest."