James Jasper (died 1868) was a British choirmaster and opium addict who owned a house on 50 Berkeley Square during the 19th century.
Living with his nephew Edward in his home, James Jasper grew jealous of Edward's betrothal to one of his pupils, Rosa, whom he shared romantic feelings for. Driven by madness, he murdered his nephew secretly and fabricated his own disappearance, hiding in his house's secret passage where he'd live on opium.
To scare other people from his home, he used levers and contraptions to create illusions of specters and ghosts. This caused the townsfolk to create legends and stories regarding the "haunted house".
Sometime in 1868, the novelist Charles Dickens and Evie or Jacob Frye investigated the house and managed to open the passage from the nearby children's key. Here, they discovered Jasper's contraptions and later, himself. Evie or Jacob managed to assassinate the madman who retold his love for Rosa and guilt for murdering Edward in his death.
- The 50 Berkeley Square memory is a reference to The Mystery of Edwin Drood, the final novel by Charles Dickens, who died in 1870 before completing it. It is generally believed that the disappearance of the titular Edwin Drood is imputable to his uncle John Jasper, an opium-addicted choirmaster who is in love with Edwin's fiancée, Rosa Bud.