The Mysteries of Paris - Volume 5 - Eugène Sue

Rodolphe, who is really the Grand Duke of Gerolstein (a fictional kingdom of Germany) but is disguised as a Parisian worker. He can speak in argot, is extremely strong and a good fighter. However he shows great compassion for the lower classes, good judgment, and has a brilliant mind. He is at ease in all layers of society and so is able to understand their problems, and how the different social classes are linked. Summary by Wikipedia