What is an allusion in The Great Gatsby, to whom does it refer, and what is its meaning?

One of the most prominent allusions Fitzgerald uses in The Great Gatsby occurs in chapter seven when Nick likens Gatsby to Trimalchio. Trimalchio was a fictional character in a work called The Satyricon written by Roman satirical writer Petronius in the first century AD. The work examines the life of the lower classes of society.

 Trimalchio was a man who had emerged from slavery and attained great wealth; he and Gatsby are similar in that both men attained their wealth themselves (as opposed to inheriting it) and both liked to show it off by hosting extravagant parties.  Fitzgerald used his novel to examine class differences among wealthy Americans, and he took inspiration from Trimalchio's nouveau riche vulgarity to create the chaotic, excessive behavior of Gatsby's parties and guests.