In The Great Gatsby by F. Scott Fitzgerald, Fitzgerald presents aspects of power in several ways. There is the power one party holds over their partner in a romantic relationship. For example, in Gatsby’s relationship with Daisy, Daisy holds power over Gatsby. This is because he is obsessed with her. She represents the unobtainable to him. In other words, she represents all that he wants: the right social class, the right background and income level, and the right girl. For Daisy, Gatsby represents a possible way out of a seemingly loveless marriage to Tom Buchanan, but he is largely a distraction for her.

Tom’s mistress, Myrtle Wilson, holds the power in her marriage to George because he loves her while she does not reciprocate his feelings:

“I married him because I thought he was a gentleman," she said finally. "I thought he knew something about breeding, but he wasn’t fit to lick my shoe.”

“You were crazy about him for a while," said Catherine.

“Crazy about him!" cried Myrtle incredulously. “Who said I was crazy about him? I never was any more crazy about him than I was about that man there.”

After Myrtle is run over and Wilson comes after Gatsby, “Wilson was reduced to a man ‘deranged by grief’ in order that the case might remain in its simplest form. And it rested there.”

There is also the power that money confers. For example, Gatsby has power of sorts over Klipspringer, who is a freeloading guest in his house. When Gatsby wants to entertain Daisy, he says, "we’ll have Klipspringer play the piano."

The power of money and the ability to cut off its source is perhaps most clearly seen in Meyer Wolfshiem. Although Gatsby introduces Wolfshiem as his friend, Wolfsheim is a business associate and, as the reader learns over the course of the book, the real black market money behind Gatsby’s house and income. As a result, Wolfsheim holds power over Gatsby.

In The Great Gatsby, power is often associated with money. He or she that has money has power. George Wilson is one of the weaker people in the novel and he is also one of the poorest. George has a run down shop and he lives in the vicinity of the Valley of Ashes, a drastically different setting than the nicer areas of East and West Egg. George's wife, Myrtle, is having an affair with Tom Buchanan. Part of the attraction, for Myrtle, is that Tom is relatively wealth. Therefore, Tom has a certain kind of power in terms of wealth and attractiveness (albeit to the shallow Myrtle) and this all stems from him having money. 

Gatsby's parties attract people because his parties have become a gathering place for social elites. They go to his parties, not because they admire Gatsby or even know him, but because the parties are a place for socializing among the wealthy and/or popular people in the city. There, people party but also make connections and in that elitist circle, the rich consort with the rich and look out for each other's well-being (mostly in terms of money): thereby, the rich stay rich and the poor stay poor. Gatsby is able to host these parties because he has a nice house which came from his own wealth. People like George Wilson would never be found at such a party, nor would he think that he might be invited or encouraged to come. 

Daisy also is attracted to money. This is part, possibly the biggest part, of the reason she married Tom. And even though Gatsby is a romantic and an idealist, he is a realist in the sense that he recognizes the power inherent in money in the social circles that he wants to live in (namely, Daisy's social circles). So, Gatsby realizes that he needs money to win her over. When he returns to find Daisy has married Tom, his idealism and romanticism remain; these qualities push him to that realist realization in that he would need money to win Daisy back from Tom. This becomes Gatsby's strategy: become wealthy, stay close to Daisy, and try to become what he thinks Daisy will admire. Note that Gatsby's romanticism and realism, the dichotomy, lead to his downfall. He is driven by that romanticism to win Daisy back, but he knows that he must have money to do so. If they were truly meant to be together, the money would not be necessary. However, in this society, the American Dream is imperfect. Gatsby resorts to illegal means to obtain his wealth. Gatsby idolizes Daisy as some perfect mate even though he must know that Daisy is attracted to money, not just the idea of love. Gatsby makes it plain that he realizes this flaw in Chapter 7 (but this doesn't seem to affect his love for Daisy). Nick begins, Gatsby responds, and Nick analyzes what Gatsby has said: 

“She’s got an indiscreet voice,” I remarked. “It’s full of——” I hesitated. 

“Her voice is full of money,” he said suddenly. 

That was it. I’d never understood before. It was full of money—that was the inexhaustible charm that rose and fell in it, the jingle of it, the cymbals’ song of it. . . . high in a white palace the king’s daughter, the golden girl. . . . 

The whole notion of Gatsby's American Dream (winning Daisy) is conflated with the idea of money and wealth. Therefore, the power to obtain this dream, among other things, is achievable through wealth. This notion makes the idealism of Gatsby's love flawed and it also suggests that success is necessarily linked to wealth, caused by it, or related to it in some way.