FACTBOX - Who was Sweeney Todd?

(Reuters) - The Stephen Sondheim musical "Sweeney Todd: The Demon Barber of Fleet Street" tells the morally complex story of a wronged barber who takes a bloody knife to patrons of his London shop.

Movie director Tim Burton has adapted the piece, with Johnny Depp in the title role and Helena Bonham Carter as his sidekick Mrs. Lovett. The film has opened in the United States and gets its British premiere on Thursday.

Here are some facts about the story and its origins:

* LITERARY BEGINNINGS:

-- For generations, scholars and historians have debated the existence of Sweeney Todd.

-- Sweeney Todd's first known appearance in print was in an 1846 "penny dreadful," a type of horror tale of the era published in serial form in "The People's Periodical".

-- The razor-wielding barber who turned his victims into meat pies was a secondary character in the short story "The String of Pearls: A Romance", written by Thomas Prest.

-- George Dibdin Pitt, a playwright of the time, dramatised Prest's story for the stage, retitling it "The String of Pearls: The Fiend of Fleet Street".

-- Pitt advertised his production one year later as "Founded on Fact." The play, set in the reign of George II, was first performed in March 1847 in London. Ever since, speculation has raged about whether the Demon Barber was man or myth.