Sweeney Todd was a serial killer.
When Clara Oswald and the Twelfth Doctor came into the Mancini's Family Restaurant, the Doctor told Clara that this was "a sort of an automated organ collection station for the unwary diner, Sweeney Todd without the pies." (TV: Deep Breath)
When Clyde Langer and Rani Chandra were in Erasmus Darkening's secret chamber in Ashen Hill Manor, Clyde told Rani that this place was creepy. According to Clyde, it was "Creepsville, Transylvania", "Hogwarts Tim Burton Style", or "Harry Potter Has A Close Shave Off Sweeney Todd". (TV: The Eternity Trap)