The title character of The Great Gatsby is a young man, around thirty years old, who rose from an impoverished childhood in rural North Dakota to become fabulously wealthy. However, he achieved this lofty goal by participating in organized crime, including distributing illegal alcohol and trading in stolen securities. From his early youth, Gatsby despised poverty and longed for wealth and sophistication—he dropped out of St. Olaf's College after only two weeks because he could not bear the janitorial job with which he was paying his tuition. Though Gatsby has always wanted to be rich, his main motivation in acquiring his fortune was his love for Daisy Buchanan, whom he met as a young military officer in Louisville before leaving to fight in World War I in 1917. Gatsby immediately fell in love with Daisy's aura of luxury, grace, and charm, and lied to her about his own background in order to convince her that he was good enough for her. Daisy promised to wait for him when he left for the war, but married Tom Buchanan in 1919, while Gatsby was studying at Oxford after the war in an attempt to gain an education. From that moment on, Gatsby dedicated himself to winning Daisy back, and his acquisition of millions of dollars, his purchase of a gaudy mansion on West Egg, and his lavish weekly parties are all merely means to that end.

Fitzgerald delays the introduction of most of this information until fairly late in the novel. Gatsby's reputation precedes him—Gatsby himself does not appear in a speaking role until Chapter III. Fitzgerald initially presents Gatsby as the aloof, enigmatic host of the unbelievably opulent parties thrown every week at his mansion. He appears surrounded by spectacular luxury, courted by powerful men and beautiful women. He is the subject of a whirlwind of gossip throughout New York and is already a kind of legendary celebrity before he is ever introduced to the reader. Fitzgerald propels the novel forward through the early chapters by shrouding Gatsby's background and the source of his wealth in mystery (the reader learns about Gatsby's childhood in Chapter VI and receives definitive proof of his criminal dealings in Chapter VII). As a result, the reader's first, distant impressions of Gatsby strike quite a different note from that of the lovesick, naive young man who emerges during the later part of the novel.

Fitzgerald uses this technique of delayed character revelation to emphasize the theatrical quality of Gatsby's approach to life, which is an important part of his personality. Gatsby has literally created his own character, even changing his name from James Gatz to Jay Gatsby to represent his reinvention of himself. As his relentless quest for Daisy demonstrates, Gatsby has an extraordinary ability to transform his hopes and dreams into reality; at the beginning of the novel, he appears to the reader just as he desires to appear to the world. This talent for self-invention is what gives Gatsby his quality of “greatness”: indeed, the title “The Great Gatsby” is reminiscent of billings for such vaudeville magicians as “The Great Houdini” and “The Great Blackstone,” suggesting that the persona of Jay Gatsby is a masterful illusion.

As the novel progresses and Fitzgerald deconstructs Gatsby's self-presentation, Gatsby reveals himself to be an innocent, hopeful young man who stakes everything on his dreams, not realizing that his dreams are unworthy of him. Gatsby invests Daisy with an idealistic perfection that she cannot possibly attain in reality and pursues her with a passionate zeal that blinds him to her limitations. His dream of her disintegrates, revealing the corruption that wealth causes and the unworthiness of the goal, much in the way Fitzgerald sees the American dream crumbling in the 1920s, as America's powerful optimism, vitality, and individualism become subordinated to the amoral pursuit of wealth.

Gatsby is contrasted most consistently with Nick. Critics point out that the former, passionate and active, and the latter, sober and reflective, seem to represent two sides of Fitzgerald's personality. Additionally, whereas Tom is a cold-hearted, aristocratic bully, Gatsby is a loyal and good-hearted man. Though his lifestyle and attitude differ greatly from those of George Wilson, Gatsby and Wilson share the fact that they both lose their love interest to Tom.