Who is Marquis de Saint-Loup-en-Bray (Robert) from Remembrance of Things Past and what is their importance?

Marquis de Saint-Loup-en-Bray (Robert) is Mme. de Villeparisis's nephew. Robert has been raised to the aristocracy but he disdains high society and the rules that he lives by. He is very well-bred and polite. He is very interested in philosophy and is kind to everyone around him.