Who is Chevalley di Monterzuolo from The Leopard and what is their importance?

Chevalley di Monterzuolo is the emissary from the newly-formed Italian government. He invites the Prince to be a participant in that government. Chevalley's sole appearance in the novel (Chapter 4, Part 2) serves as a trigger for the Prince's important, character-revealing speech relating to the nature of Sicilian life and perspective, a speech that gives important insights into the Prince's personal character as well.