Sweeney Todd is a villain appearing in various English language works starting in the mid-19th century as a barber and an early example of a serial killer. His weapon is a straight razor (or cut-throat razor in British English), with which he slits his victims' throats. In some versions of the story Mrs. Lovett, who is his partner in crime and variously his friend or lover (and whose first name is variously Marjorie, Sarah, Nellie, Shirley or Claudette) hides the crimes by butchering the corpses of Todd's victims, baking their flesh into meat pies, and selling them to unknowing customers. He is also assisted by an unwitting apprentice lad named Tobias Ragg, who later aids in unmasking his crimes. In most recent versions of the story, Sweeney either helps or hinders (sometimes both) the love affair of a young woman, Johanna Oakley and a sailor named Mark Ingesterie or more commonly known as Antony Hope. In the musical stage production and 2007 film, Johanna is Todd's daughter Johanna Barker.

Sweeney Todd may not be a wholly fictional character. In two books, Peter Haining argues that Sweeney Todd was an historical figure who committed his crimes around 1800. Nevertheless, other researchers who have tried to verify his citations find nothing in these sources to back Haining's claims. There is, however, a similar story reputed to have occurred on the Rue de la Harpe in Paris that likely influenced the stories of Todd as well. "newspaper account of a barber on Fleet Street in 1784 commiting a single murder" PBS.org.