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, dramatized Prest's story for the stage, re-titling 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.

* MAN OR MYTH?

-- No public records substantiate the existence of a London barber named Todd in the late 18th century or, for that matter, of a barber shop located on Fleet Street.

-- However there was certainly enough real-life horror around at the time, reported in "The Old Bailey" section of the London Times, as well as other daily newspapers.

-- As news commonly traveled by word of mouth (much of the population was still illiterate), stories of shocking criminal exploits passed from person to person with probable embellishment along the way and were asserted to be "true fact."

* THE MUSICAL:

-- The musical, composed by Stephen Sondheim was based on Christopher Bond's retelling of the String of Pearls. It opened on Broadway in March 1979 and ran for 558 performances until June 1980.

-- The London production opened in July 1980 and ran for 157 performances at the Drury Lane Theatre.