The Great Gatsby is a work of fiction, but there are true elements in the story. For instance, the character of Meyer Wolfsheim is, allegedly, based on a real world figure, Arnold Rothstein, who was a member of organized crime in New York and was subsequently instrumental in moving it into areas beyond New York, including into the Las Vegas gambling industry.
In the book, Meyer Wolfsheim is a member of the underworld who is a friend of Gatsby's. It is largely through Wolfsheim that Gatsby has attained his fortune in ways that the reader is led to believe are illegal. Gatsby tells Nick with some pride that Wolfsheim was behind the scheme to fix the 1919 World Series. Like Wolfsheim in the book, Rothstein was suspected of having been the architect behind fixing the 1919 World Series, bribing members of the Chicago White Sox team to deliberately lose the game.
Moreover, there are also autobiographical or semi-autobiographical elements in the book. For instance, the character of Daisy Buchanan, Gatsby’s love, likely was at least partially based on F. Scott Fitzgerald’s own wife, Zelda. Like Daisy, Zelda was born into a prominent southern family and was considered a socialite. Fitzgerald, in comparison, was from much humbler origins and was keenly aware of his exclusion from the wealthy upper classes.
Just as in the book, wherein Daisy and Gatsby meet at a party while he is a soldier, Fitzgerald met Zelda at a country club dance when he was an officer stationed nearby. Daisy is very conscious of class and wealth in the book, which leads her to marry Tom. In a similar vein, Zelda was worried about Fitzgerald's financial prospects and hesitated for a while before agreeing to marry him.
Although Gatsby never marries Daisy in the book, the turbulent end to their relationship might also reflect the turbulence that marked the Fitzgeralds’ marriage, which was marred by heavy drinking, Zelda’s mental illness, and long periods during which she was institutionalized.