Jim Williams represents a common theme in MGGE, which is preservation. He is a seller of antiques in the Mercer House, however, instead of selling things from a store, he surrounds himself (at home) with the antiques that he sells, indicating his desire for preservation of past culture.
Additionally, by selling antiques, it shows that he wants to spread this idea to those who buy the antiques themselves.
Jim Williams represents the culture of Savannah because when he reveals his sexuality and that Danny was his lover, the community is surprised (indicating the secretive nature of Savannahians) , however accepting of differences in their town.
Jim Williams lives alone in Mercer House, where he remains solitary/isolated , with the exception of throwing his annual parties. Williams showcases the theme of isolation perfectly, as he rarely deals with affairs outside of Savannah, and he chooses to live in physical isolation as well.