To the public eye, Jack is an art consultant who analyzes and determines the value of fine art. He helps James Moriarty obtain the paintings he desires, regardless of whether the method of doing so is legal or not. Secretly, Jack serves 'M,' the criminal organization created by James, alongside Sebastian Moran and lives with the two of them in James' estate.
Jack has shoulder-length, light brown hair and dark red eyes. He wears a red and black coat decorated with a blue rose lapel pin, a symbol of his membership in 'M.' Underneath his coat is a dark blue vest layered over a white long-sleeved shirt.
According to Sherlock Holmes, Jack is a psychopath and sadist. The idea of crime and homicide excites him and he often jokes about death, though it is sometimes difficult to determine whether he is actually serious or not. He developed a strong disdain for women as a result of the lack of affection from his mother. He sees his murders as works of art and tends to choose older women as his victims. He despises murderers who copycat his method and has no hesitation in killing them to set an example.
Despite his malicious tendencies, Jack is adept at hiding them and can appear normal to those unaware of his true personality. Although Jack may promote seemingly reckless behavior, he is intelligent and calculating, allowing him to be skillful when it comes to playing card games, such as poker. He is also very perceptive of his surroundings and with reading people, and he has an uncanny ability to detect someone's presence. He's also a skilled hypnotist.
- In the original stories from Doyle, Sherlock never encounters Jack the Ripper and the murders are never mentioned, but it's become a popular fiction in today's culture.