Jack the Ripper wasn't the first serial killer, or the worst. But at that time the British Empire was the world's superpower and London was, essentially, the capitol of the world. Since the London Times was read pretty much everywhere in the world, everyone heard about Jack.
Jack the Ripper? Dear me, where do I start? There are at least two full-length novels, probably more, including Michael Dibdin's "The Last Sherlock Holmes Story", in which Holmes himself is the Ripper. This idea is based on the assumption that Holmes habitually wore a deerstalker hat (actually, in the stories he never specifically does, though some early illustrators chose to show wearing one some of the time; however, wearing a specifically rural hat all the time in Victorian London would have been so odd that Holmes might as well have worn a tinfoil beanie), and one eyewitness description of a man who might possibly have been JTR has him wearing a deerstalker.
M. J. Trow's novel "The Adventures of Inspector Lestrade" plays with this, making the Ripper suspect in the deerstalker Holmes, an overrated amateur detective who draws the attention of the police with his silly disguise (historically accurate - at least one amateur detective in a ridiculous disguise was arrested as a Ripper suspect after locals reported him for suspicious behavior). In Trow's version of the story, Holmes is a minor character who deduces the famous but far-fetched Masonic theory (popularized as fact by Stephen Knight, and picked up on by Alan Moore because it suited his personal beliefs, but very, very unlikely indeed to be even partly true), but he turns out to be totally wrong.
The famous Goulston Street Graffito, which read "THE JUWES ARE THE MEN THAT WILL NOT BE BLAMED FOR NOTHING", may or may not have been written by Jack, but probably wasn't, since antisemitic graffiti in the East End wasn't especially unusual at the time. The word "Juwes" has absolutely no Masonic significance whatsoever - some illiterate racist just couldn't spell "Jews". Though a hastily-scrawled "JUIVES" in capitals is almost identical to "JUWES", suggesting that, if he really did write it, the Ripper was both antisemitic and French.
There was at the time in England a tradition of semi-mythical bad guys being called "Jack", apparently starting with the 18th. century highwayman Seven-String Jack (though he probably took it from the totally mythical Jack-in-the-Green, Jack -o-Lantern, and other mischievous supernatural creatures), and gained a huge boost from the legendary Spring-Heeled Jack, who some people believed was in fact Jack the Ripper, which would have made him about a hundred years old, and therefore a supernatural being. Which of course explained why the police couldn't catch him.
It's worth mentioning that, before he was called Jack the Ripper, Jack (who was at the time assumed to have killed several other prostitutes before the canonical five) was nicknamed Leather Apron, a semi-mythical terror who did actually exist. He was in reality a deeply unpleasant bully called Jack Pizer who, being a cobbler, habitually wore a leather apron and carried sharp knives. He also supplemented his income by threatening to "rip" prostitutes of the lowest kind (who had no pimp to protect them) if they didn't give him a few pennies from their pitiful earnings. The discovery of a leather apron at the scene of the second murder (the presence of which turned out to be purely coincidental) added fuel to the flames. Although he doesn't seem to have ever actually hurt anyone, his bluff was convincing enough for the police to pick him up after the first two murders. They found him hiding in a relative's house in terror of a lynch-mob - he was almost glad to be arrested. Then, when the "Double Event" occurred while he was still in custody, he was released and totally forgotten about by everybody, making him the Pete Best of Ripperology, despite having a fairly cool supervillain nickname. I'm not sure if Leather Apron fits any tropes, but it's interesting, isn't it?
What was so special about Jack?
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