who is the cruelest character?

I would say that might be Danglers. Danglars is the mastermind behind the letter, which incriminates Dantes. He becomes captain of the Pharaon once Dantes is imprisoned. He becomes a banker with an incredible fortune and a Baron. He has one daughter, Eugenie. His wife and he are alienated, especially when his wife, as money hungry as he, ruins part of his fortune. Monte Cristo ruins the other half. He destroys Danglars by destroying his fortune.