As you read in the book, you will find that the one reason he goes and tries to prosper is because he wanted to marry a girl called daisy but he couldn't because he was poor. That's were his dream comes in. Because he was born into a poor life, his dream was that he could one day become rich.
And when he does achieve it, that reflects the "American Dream". But his dream was also his downfall. His obsession with the past (his love for daisy) is what kills him.
He wanted the relationship he had with her in the past to last forever and he couldn't see that part of his attraction to daisy in the first place was because of what she represented for him: money and the upper class.
In a way, he thinks if he can get daisy to love him, he can prove to himself that he belongs to the upper class.
He embodies that American idea that no matter where you come from, even if your poor you can become anything you want.
But what the book suggests is that this idea of the American dream is some kind of a lie because Gatsby has to resort to crime and murder to pursue his dream.
The figurative as well as literal death of Jay Gatsby in the novel The Great Gatsby symbolizes a conclusion to the principal theme of the novel. With the end of the life of Jay Gatsby comes the end of what Fitzgerald views as the ultimate American ideal: self-made success. The intense devotion Gatsby has towards his rebirth is evident by the plans