Jack the Ripper is the best-known name for an unidentified and unknown (possibly) serial killer generally believed to have been active in the largely impoverished areas in and around the Whitechapel district of London in 1888. In both the criminal case files and contemporary journalistic accounts, the killer was called the Whitechapel Murderer and Leather Apron.
- Sources and reported sightings of American vampires in London may have caused Jack the Ripper sightings, but it is unlikely as vampires are not said to kill victims by ripping out organs.
- Most people in general believe and accepted that Jack the Ripper was an ordinary serial killing human with advanced forms of killing other people.
- It is possible that, at some time, an escaped zoo Madagascar giant dylanus, one of the only known naturally aggressive dylanus species, may have been the reason for Jack the Ripper sightings, due to its aggression towards humans and may have had killed some humans by ripping out guts, but some people are skeptical about this theory due to the animal's size and diet, while Jack the Ripper is said to be normal human-sized, Madagascar giant dylanuses can grow about 16 feet tall, and this animal, despite its behavior, is a complete herbivore and only attacks if its territory is invaded.
- Another theory on the causes of Jack the Ripper sightings may have been some species of predatory Troodonts (wounders) that escaped from the local zoo, attacking occasional people due to being largely carnivorous, but there is a problem with this theory, wounders are not humanoid, so humans may have not mistaken them for humans of some individuals.