Spring-heeled Jack is an entity in English folklore of the Victorian era. The first claimed sighting of Spring-heeled Jack was in 1837. Later sightings were reported all over Great Britain and were especially prevalent in suburban London, the Midlands and Scotland. There are many theories about the nature and identity of Spring-heeled Jack. This urban legend was very popular in its time, due to the tales of his bizarre appearance and ability to make extraordinary leaps, to the point that he became the topic of several works of fiction. Spring-heeled Jack was described by people who claimed to have seen him as having a terrifying and frightful appearance, with diabolical physiognomy, clawed hands, and eyes that "resembled red balls of fire". One report claimed that, beneath a black cloak, he wore a helmet and a tight-fitting white garment like an oilskin. Many stories also mention a "Devil-like" aspect. Others said he was tall and thin, with the appearance of a gentleman. Several reports mention that he could breathe out blue and white flames and that he wore sharp metallic claws at his fingertips. At least two people claimed that he was able to speak comprehensible English.
- Sources and reported sightings of American vampires in London may have caused spring-heeled Jack sightings.
- Some people believe that spring-heeled Jack may have been an ordinary person, but here is a problem to this theory, no natural human could leap in a way this being could have done, if he existed.
- Some people said that he may have been a demon or a ghost.
- 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 spring-heeled Jack sightings, but there are three problems with this guess, number one, this animal is far to big to fit the spring-heeled Jack's description, two, this animal is purely herbivorous and only attacks any non-dylanus intruders if its territory is invaded, and three and most importantly, this species cannot jump due to its gigantic size.
- Escaped zoo kangaroos make likely candidates for spring-heeled Jack sightings due to their high-jumping abilities and at first first glance they can look like humans, except for one problem, they aren't known to talk, not even simple speech.
- Some species of predatory Troodonts (wounders) that escaped from zoos are the most likely explanation for spring-heeled Jack sightings due to their jumping abilities, having reported to have somewhat speak English (which some wounder species can due to their intelligence, their advanced parrot-like vocal cords, and people training these dinosaurs to talk), and being said to have resembled a humanoid demon at first glance, with their clawed wings often being misinterpreted as a cape with human arms.