The Master of Lake-town (which is also known as Esgaroth) is like the mayor. Lake-town is the last town near the Lonely Mountain, and it sits on Long Lake. So when Thorin & Co. emerge from the Elvenking's barrels, they come up in Lake-town. The Master of Lake-town sees that his people are really excited about the reappearance of the King under the Mountain, so he makes a big fuss out of supporting Thorin and giving him feasts and supplies and all that. But he's also certain that Thorin is a phony going to his own death.
So the Master of Lake-town is a bit of a hypocrite. He may be a shrewd businessman, but he's also quite deceptive. Roäc the raven sees this quality in the Master and warns Thorin, "If you will listen to my counsel, you will not trust the Master of the Lake-men" (15.20). And this mistrust proves justified way down the line. When Balin comes to visit Bilbo at the end of the novel, he tells our hobbit that the Master of Lake-town has "come to a bad end" (19.33). He received many riches from Bard after Smaug's death, but "he fell under the dragon-sickness" (19.33). In other words, he gets really greedy, runs away with as much gold as he can snatch, and dies alone of starvation in the wilderness.