Gatsby starts off as the stereotypical poor boy with dreams of making it big. He idealism money, beauty, and prosperity, all of which are seen in his "love" Daisy. Gatsby starts off doing whatever needs to be done in order to fulfill his dream of being rich and marrying Daisy. He is very disillusioned in the beginning, refusing to see obstacles that stand before his dream (such as Daisy being married, or the coming consequences for his less than honorable means of getting money). At the end of the story, he finally sees the world for what it is. He realizes that Daisy will never leave Tom, and that all his dreams are just that, dreams.
In F. Scott Fitzgerald's "The Great Gatsby," Jay Gatsby's greatness lies in his capacity for illusion. When this illusion is destroyed, then, Gatsby "transforms" into a tragic character. Thus, through his character Jay Gatsby, Fitzgerald develops his theme of Appearance vs. Reality as well as his criticism of the "American Dream" as the desire of mere materialism.
Representative of the American Dream, Gatsby is a self-made man who came from humble beginnings to wealth and position. He is youthful and resourceful. However, accompanying this American Dream of Gatsby is the underlying corruption which leads to his tragic demise. For, Gatsby allows himself to be exploited in several ways. First of all, he is exploited as he allows the fashionable people to partake of his parties, food, and home; however Gatsby tragically believes that he is rising in society. That this is but an illusion is suggested by Nick's alluding to Gatsby as the mythological character Trimalchio, the giver of lavish parties. Then, he is further exploited by Daisy who does not truly love him; she simply has been infatuated with his appearance that is different from what she has known. Of course, the final exploitation of Gatsby is his being implicated by the villainous Tom Buchanan as the murderer of Myrtle Wilson by manipulating Wilson's conviction that Gatsby is the lover of his wife.
While all the others are guilty of malfeasance in their pursuit of the American Dream--Meyer Wolfsheim's design for wealth is criminal, the Buchanans desire for the good life victimizes others to the point of murder, Jordan Baker cheats to achieve her fame--Gatsby is the only idealistic, unselfish character in the novel. And, for this reason, he becomes tragic as his dreams are naive illusions.