The dragon of Smaug is most known for his greedines as it stole the tresure in the Lonely Mountain from Thorin's ancestors. It can be presumed though that he was greedy before hand. Bilbo and Thorin a change occurs before the readers eyes as they go from themselves to greedy and cocky. I believe this is from the site and feeling of the emmense amount of treasure in the cage. The tresure was described to be so large that the dwarf party couldn't believe their eyes.
When Bilbo enters the cave the first time there is definant change in his personality. During his long walk he starts to talk about how such a great theif he is and how he is the leader of the group and asks himself why he's even with them. Once he exited the cave with the cup he returns to his normal self for the most part, fairly modest and not cocky.
On the other hand Thorin under went a similar change when he first saw the tresure. His level headedness evaporated as he became an obsessed greedy dictator. He no longer cared what others had to say or felt, he only cared about himself. He did not feel the village people deserved any of the tresure despite their service in killing the dragon. The tresure was in a way evil.