Dan Cody is a wealthy copper mogul whom Jay Gatsby saves. In gratitude, Cody hires Gatsby as a personal assistant and introduces him to a life of wealth and luxury. Symbolically, Cody represents the lifestyle and wealth that Gatsby wants. Although Cody leaves Gatsby $25,000, his mistress prevents Gatsby from inheriting the money, creating an obsession with amassing wealth and surrounding himself with luxury.
Cody is a relatively minor character whose generosity and gratitude inadvertently increase Gatsby's sensitivity towards his own lack of wealth and status. Before he and Gatsby meet, Gatsby is working as a janitor for the college. By saving Cody and experiencing the luxury of his life, Gatsby is abruptly confronted with the stark difference between himself and Cody as well as between Gatsby and Daisy Buchanan.
Cody and Daisy share a similar role of representing the wealth and luxury for which Gatsby longs. It's briefly mentioned that Gatsby keeps a portrait of Cody in his house, demonstrating the vast influence the man has on Gatsby and acknowledging the role he plays in diverting the course of Gatsby's life. Working as Cody's personal assistant taught Gatsby the manners of the upper class and helped a young James Gatz create the Jay Gatsby persona.