In *The Hobbit*, [the Dwarves, Bilbo and Gandalf are on a mission to rob Smaug][1]. But why this Dragon has so much to steal from? It's a Dragon! He is not the kind of dragon that [eat gold and gems][2]. He doesn't need wealth to buy a luxury cavern and or pay his servant. 

Why Smaug gathered his treasure?

  [1]: http://scifi.stackexchange.com/questions/3726/why-was-gandalf-involved-with-the-dwarves-mission-to-rob-smaug
  [2]: http://scifi.stackexchange.com/questions/23645/why-does-spike-eat-gems-in-my-little-pony-friendship-is-magic