The term 'Stevenson Character' refers to two characters from the novel 'Strange Case of Dr. Jekyll and Mr. Hyde' by Robert Louis Stevenson. The first character is Hyde, a mysterious figure who is the dark alter-ego of the protagonist, Dr. Jekyll. The second character is Jekyll himself, a scientist who creates a potion that transforms him into Hyde. The third character is Mr. Hyde, the name Jekyll takes when he is transformed into his darker self. All three characters are integral to the story and represent the duality of human nature.