The Mysteries of Paris - Volume 1 (version 2) - Eugène Sue

Rodolphe is the Grand Duke of Gerolstein, a fictional kingdom of Germany, but disguises himself as a Parisian worker. He can speak in the secret language of criminals, is extremely strong and a good fighter. However, he shows great compassion for the lower classes, good judgment, and has a brilliant mind. In the story, he moves through different layers of society, and understands their problems and how they are all linked. (Modified from Wikipedia)