Leonard Joseph Cariou is a Canadian stage actor, singer and stage director. He gained prominence for his portrayal of Sweeney Todd in the original cast of Stephen Sondheim's musical Sweeney Todd: The Demon Barber of Fleet Street (1979) alongside Angela Lansbury for which he won the Tony Award for Best Actor in a Musical. He also received Tony nominations for his roles in the Betty Comden and Adolph Green musical Applause (1970), and the Sondheim musical A Little Night Music (1973).

Sweeney Todd is a fictional character who first appeared as the villain of the penny dreadful serial The String of Pearls (1846–1847). The original tale became a feature of 19th-century melodrama and London legend. A barber from Fleet Street, Todd murders his customers with a straight razor and gives their corpses to Mrs. Lovett, his partner in crime, who bakes their flesh into meat pies. The tale has been retold many times since in various media.