Thaddeus Smith (unknown – 1868) was a British citizen, who lived and worked in cities around the world in the mid-nineteenth century.

Alongside his associate, Dr. Wilburn, Thaddeus Smith performed séances around the world, using different stage names in every city. After swindling his clients, as well as their manipulative relatives and friends, Thaddeus would expose them, followed by his own faked death. He and his associate would then move to a different city and perform the same swindle again.

By 1868, Thaddeus and Wilburn had performed their swindle in Boston and Sydney, and had arrived in London. There, Thaddeus gained a small circle of clients - Howard Roberts, Janice Asquith, and Lady Ursula - whom he was swindling. Meanwhile, Anne Roberts, Everett Boyd and Douglas were also paying him, going behind the backs of those close to them to get what they wanted.

Anne and Douglas, however, discovered the swindle Thaddeus tried to pull off by reading about his previous swindles in the newspaper. Being present at the séance, Douglas made use of the darkness when the lights went out, and stabbed Thaddeus in the neck, preventing his own swindle from being brought to light.

Jacob or Evie Frye, both Assassins, investigated the murder of Thaddeus the Great, interrogating all of his clients and surmising that Douglas was the murderer. When confronted, Douglas confessed to the crime, explaining that Thaddeus had gotten what he deserved for trying to out a fellow crook.