The irony is that if Smaug not been bragging about his "diamond waistcoat" of impenetrable scales, Bilbo never would have seen the hole in it. Bilbo communicated this (by means of the Thrush) to Bard the Bowman, and with that information, he was able to slay the dragon with a well-placed arrow. As is common in mythology, Smaug was killed by his own hubris.
Chat with our AI personalities
The killer of Smaug is Bard the Bowman. He's alerted by a thrush who overheard of Smaug's weakness (a single bare spot in his bejeweled chest).Bard, a man in the town of Esgaroth, a town by the lake, killed the dragon. He was told by the thrush where Smaug's weak spot was, and thus Bard was able to shoot the dragon through the heart.
Smaug takes a snooze. Z Z Z Z Z (Smaug)
Bard shoots Smaug with his black arrow.
Smaug the Golden (with some red I believe).
Bard the Bowman shot a black arrow into the bare hollow in Smaug's left breast, killing the dragon. The arrow was believed by Bard to have come from the King Under the Mountian, and his father and his grandfather had used it.