Who is Ferguson from The Innocents Abroad and what is their importance?

A. Billfinger is a professional tour guide in Europe. Twain found his name so preposterous that he and his companions renamed him Ferguson. At first, Ferguson is very professional. Unfortunately, the group soon discovers that he is greedy, and that he is taking advantage of them to line his own pockets. Over the course of the novel, the reader comes to realize that there isn't only one Ferguson, and that each of the guides Twain meets along the way are addressed as such.