Nick represents the stereotypical responsible citizen, accepting of other peoples' faults while understanding the price they are paying for the apparent advantages they have. Nick's Midwest values and honest work ethic make him the closest to a solid, mature human being in the group.
Jay Gatsby is the ultimate example of the self-made man, although his story ends in tragedy. He creates the fantasy family from which he claims to have come, never gives up the dream of winning Daisy for himself, uses wealth gained from crime to build himself what he imagines will be a fabulous and fulfilling lifestyle - and eventually looses it all.
Tom is a bully in every sense of the word. He is racist, uses his wealth to intimidate others, and becomes physically aggressive easily.
Daisy is the airhead, the beautiful blonde with no common sense or interest in anything other than enjoying her materially comfortable life with her beautiful friends.