The classic novel "Dr. Jekyll and Mr. Hyde" by Robert Louis Stevenson is often associated with themes of duality, the doppelgänger, and the struggle between good and evil. Synonyms for the title include "The Strange Case of Dr. Jekyll and Mr. Hyde," which emphasizes the enigmatic quality of the story, as well as "The Dual Nature of Man," which highlights the central conflict between the character's two personas. Other possible titles might encompass the themes of transformation, identity, and morality, such as "The Two-Faced Man," "The Split Personality," and "The Conscience of a Monster." Each of these titles highlights different aspects of this complex and thought-provoking story.