In the Great Gatsby, why does Fitzgerald tell the story of James Gatz?

The James Gatz story is important for at least two
reasons. First, readers are trying to keep track of truth and lies in this story, and
the James Gatz story is a guaranteed truth as it comes from our author, not a biased
character.

Second, this story of his background gives merit
to the idea that Gatsby is in pursuit of finding his identity. A name change suggests a
complete and total change of a person, and we can see that as the James Gatz character
was not too successful, while the Jay Gatsby character is extremely successful. At one
point, Nick narrates,

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"It was James Gatz who had been loafing along
the beach that afternoon in a torn green jersey and a pair of canvas pants, but it was
already Jay Gatsby who borrowed a rowboat, pulled out to the Tulomee,
and informed Cody that a wind might catch him and break him up in half an
hour."

James Gatz went from a
17-year-old who lacked confidence to a 17-year-old entrapaneur taking a risk to initiate
conversation with an obvious wealthy man who had no concept of a potential upcoming
gale.

Later Nick notices about the emerging
Gatsby:

"But
his heart was in a constant, turbulent riot. The most grotesque and fantastic conceits
haunted him in his bed at
night."

The new Gatsby
character was taken with his imagination and believed in a glorious and fantastic
possible future.

This entire section is important because
Gatsby is an everyman in many ways. All mankind dreams about what more could come in
their lives. The restless discontent of Americans with the status quo is ever present.
This story of James Gatz demonstrates that in Gatsby's life, there was a defining moment
which forever changed him from the sweet lakeside boy to the ambitious American
dreamer.