After a bit of searching, I found this quote from http://www.book-of-thoth.com/article943.html:
"It is thought that the original Spring-Heeled Jack (for there was obviously more than one) was an Irish nobleman, The Marquis of Waterford, who was renowned for his sadistic taste in practical jokes, and his scorn for women. Author Peter Haining in his book "The Legend and Bizarre Crimes of Spring-Heeled Jack" believes that Waterford’s idea for the character of Jack was brought about by a humiliating experience with a woman and a police officer while travelling abroad.
Haining believes that Waterford and his rich friends thought up the idea as a prank to get even, by proxy, with the police and women in general. Haining also believes that Waterford (who had friends who studied applied mechanics) helped him invent "spring-heeled boots" (boots with powerful springs in the heels) to help him with his attacks.
It is likely that he also learned the technique of the fire-eater in order to heighten the supernatural aura of Spring-Heeled Jack. In addition, Waterford had strangely protuberent eyes, which matched the descriptions of Jack. He was also in the area when many of the attacks occured. As a final piece of evidence, the servant boy who scared Jack away saw a crest with the letter "W" on the man’s cloak.
Although the mystery of Spring-Heeled Jack’s identity has probably been ascertained, it is far more entertaining and romantic to think of Spring-Heeled Jack as a mysterious creature of the night who may someday leap from the shadows again. "
According to reviews, Haining's book, 'The Legend and Bizarre Crimes of Spring-heeled Jack', takes an investigative approach to the cases. "Instead of the brief and confusing anecdotes in other books, Haining's attention to factual detail and considerable story-telling prowess makes for a gripping read.
Haining also covers the other weird events linked to SHJ, and debunks more farcical theories in favour of a reasoned approach. His conclusion that the Maquis of Waterford WAS Spring Heeled Jack is hard to dismiss. "
However, another reviewer gave a less praising, and even more skeptical review, stating, "It is more or less useless as a reliable study.
To take only a couple of examples, Haining reports Jack's most famous assault - on Jane Alsop, in Old Ford, in February 1838 - solely from a single well known report published by The Times two days after the attack. He was evidently unaware that two more, much longer and more detailed, follow up reports appeared in the same newspaper on 2 and 3 March. These later accounts not only detail the results of the police and local magistrates' investigations into the Alsop case, but give the names and evidence of suspects who were brought to court for questioning."
Bottom line, I don't think there's a whole lot of substance to the SHJ stories, apart from a number of very well-performed pranks and attacks.
