Jack the Ripper

Jack the Ripper was the name given to a serial killer who terrorised London in 1888. Several entities were believed to be the source behind the killings.

Potential Suspects
The Valeyard was said to have committed the killings in order to power the Dark Matrix. In an alternative timeline, the killings continued, leading to anarchy in London. (PDA: Matrix)

Other accounts claimed that the Fellowship committed the murders in an attempt to summon the Yssgaroth into the universe. (NA: The Pit)

A third account claimed the Ripper was a Re'Nar shapechanger who was killing in order to place blame upon a rival race. It was eventually stopped by the Eleventh Doctor. (IDW: Ripper's Curse)

Other References

 * Jack the Ripper was believed to be caught by the Silurian Madame Vastra, who proceeded to devour him. She found him "stringy, but tasty all the same". (DW: A Good Man Goes to War)
 * The Fifth Doctor planned to investigate the mystery of Jack the Ripper's identity for the use in his book Doctor Who Discovers Historical Mysteries. (BFA: The Kingmaker) By his Eighth regeneration, he believed he knew Jack the Ripper's identity. (EDA: The Bodysnatchers, Interference - Book Two)
 * Chris Cwej believed he knew Jack the Ripper's identity. (BNA: Dead Romance)
 * In an alternative timeline, the Valeyard used the knife which had belonged to Jack the Ripper. (DWU: He Jests at Scars...)