There are many similarities among Fitzgerald, Nick, and Gatsby. All are sons of the Midwest, and both Nick and Gatsby served in WWI, something Fitzgerald wanted to do before the Armistice ended his chances to earn the medals of which Gatsby was so proud. It is fair to say that each is a member of the Lost Generation: Fitzgerald as an often expatriated artist and Nick and Gatsby as restless war veterans eager to start new lives.

Nick Carraway is, like Fitzgerald, a writer. As such, both are keen observers of the lives of others while retaining elements of being an outsider. Nick participates in and records the events of the tumultuous summer he spends on Long Island but maintains a separateness because he knows he does not truly belong in that milieu. Fitzgerald was often in similar circumstances, perhaps beginning with his time at Princeton. He was not the academic or socioeconomic equal of the majority of his classmates and no doubt often felt like an outsider.

A college romance with a wealthy and socially prominent debutante, Ginevra King, was doomed in much the same way as Gatsby's romance with Daisy Fay. Ginevra King's father is reputed to have told Fitzgerald that "poor boys shouldn't think of marrying rich girls," a motif that runs through many of Fitzgerald's short stories and novels. It is clear that Ginevra King and Daisy Fay are both iterations of the "golden girl" that was out of reach for Fitzgerald. It has been written that Zelda Sayre, Fitzgerald's wife, broke off their engagement when the full picture of his poverty was revealed to her, and that she only changed her mind when he had an overnight success with his first bestselling novel.

In the climactic seventh chapter of The Great Gatsby, Tom Buchanan brutally reminds Jay Gatsby of his inferior social status by saying "I'll be damned if I see how you got within a mile of her unless you brought the groceries to the back door" with regard to his wife, Daisy. Fitzgerald seemed to realize that while wealth can be acquired, social class is something that one is born into and that one's roots do tend to define one's social trajectory.

Is The Great Gatsby autobiographical? Is Fitzgerald more like Nick or Gatsby?

Fitzgerald's The Great Gatsby, like any modern or post-modern novel, is a mix of autobiography, fiction, non-fiction essay, poetry, and play.

Fitzgerald is a mix of Nick, Gatsby, and even Tom.  His wife Zelda more closely matches up with Daisy than he does with his characters.

In terms of morality (ethos; superego), Fitzgerald is like Nick.  They are both from the midwest.  FSF came to New York and was disillusioned there and then returned to the Midwest for a spell.

In terms of lifestyle (pathos, id), Fitzgerald is like Gatsby.  FSF lived fast and died young (44).  He was a dreamer like Gatsby.  He traveled to Europe like Gatsby.

In terms of marriage, Fitzgerald is like Tom.  Both married women who were "hopeless little fools."  Zelda was more unstable than Daisy; she was in mental institutions.  FSF also had women on the side, like Tom.