"Jack the Ripper" is the popular name given to the serial killer who killed a number of prostitutes in the East End of London in 1888. The name originates from a letter written by someone who claimed to be the killer published at the time of the murders. He was also called the Whitechapel Murderer and "Leather Apron."
The name "Jack the Ripper" was first used in the 'Dear Boss' letter and gained worldwide notoriety after its publication.
http://www.casebook.org/images/dearboss2_big.j pg
Most of the letters that followed copied the tone of this one. After the murders, police officials contended the letter had been a hoax by a local journalist along with hundreds of others that were received.