Jay Gatsby is Nick Carraway's extremely wealthy neighbor. He lives in a magnificent mansion in the West Egg, directly across the sound from the Buchanan estate. When Jay Gatsby returned from the war, he became business partners with Meyer Wolfsheim and amassed a fortune in the illegal bootlegging industry. He never lost his love for Daisy, and he purchased an extravagant mansion directly across the water from her home. Gatsby knew that Daisy had married Tom Buchanan, but he still held onto his dream of one day marrying her.
In an effort to reconnect with Daisy, Gatsby hosts elaborate parties, where strangers from all over the East and West Egg are invited. Interestingly, Gatsby does not participate in the revelries taking place at his home but passively watches over his parties as a host, hoping that Daisy will attend. At the end of chapter four, Jordan Baker explains to Nick how Daisy and Jay Gatsby originally met. She then mentions the reason why Gatsby hosts elaborate parties at his mansion, telling Nick,
I think he [Gatsby] half expected her [Daisy] to wander into one of his parties, some night . . . but she never did. Then he began asking people casually if they knew her, and I was the first one he found. It was that night he sent for me at his dance, and you should have heard the elaborate way he worked up to it. (Fitzgerald, 85)
Overall, Jay Gatsby hosts elaborate parties at his mansion in the hopes that Daisy Buchanan will attend one of the parties and they will finally reconnect.