Slenderman

Justin Parkinson has a BBC article about a mystery killer:

Two stabbings in the US have been linked to the fantasy horror character Slender Man. Who is he? The Know Your Meme site defines Slender Man, or Slenderman (illustration), as "a mythical creature often depicted as a tall, thin figure wearing a black suit and a blank face". In the mythology "he can stretch or shorten his arms at will and has tentacle-like appendages protruding from his back".
Representations of Slender Man can be seen in many guises. On the Etsy craft sales website, there are key rings, bracelets, and stuffed toys. On Flickr and Instagram, you can see everything from Slender Man fancy dress to Lego tableaux. Hundreds of thousands click on YouTube videos based on the character. He crops up on blogs in graphic art and fan fiction. Every depiction riffs on the central characteristic of the black suit and blank face. And the thinness.
The Slender Man meme began in June of 2009, when a competition on the comedy web forum Something Awful asked for ideas for a modern myth with which to terrify people. One contributor, Eric Knudsen, using the pseudonym Victor Surge, responded by posting two faked photographs, purportedly from the mid-1980s, showing a tall, sinister figure lurking behind groups of children. Knudsen attached some vague text suggesting fourteen young people and the photographer had gone missing. From the very beginning it was intended to be a meme, in the original sense of a replicating idea. Knudsen's fragmented post prompted a creative outburst. Eventually thousands of people were making drawings and writing stories. Slender Man has appeared in video games, while Marble Hornets, the YouTube series featuring stories about him, is followed by more than half a million people. One academic has described his development as an "open-sourcing of storytelling".
"It just exploded. It became a phenomenon that I don't think anybody could have predicted," says Jeff Tolbert, a folklorist from the University of Indiana, who has written about Slender Man.
The character almost seems to be an amalgam of knowing winks to both internet and pre-internet culture. Like folk villains over the centuries, from the Big Bad Wolf to the Headless Horseman, Slender Man is often depicted standing in the woods. His tentacles conjure up fleeting hints of HP Lovecraft's world of interdimensional monsters in ordinary settings. The black suit nods at the Matrix villains, Jack Skellington from The Nightmare Before Christmas, and even the Hitman video game series. But all those could, of course, be coincidental.
Fans of the character can hold strong views about the way it should be used. "There were a few instances where someone would try to take Slender Man in a different direction," says Tolbert. "One came up with a story of a military group trying to track him. Other users didn't like that idea. It was too obvious. It lacked subtlety. It was more like an X-Files story than a proper myth. There is a sort of consensus about Slender Man. People collectively take on some bits and reject others."
Many of the fan stories have ended up on the Creepypasta website, where paranormal stories are shared, delivered as if they are true, rather in the fashion of campfire tales.
But mainstream media attention for the phenomenon has been scant up until now. There was a brief spike of interest in the summer of 2012, according to Google Trends, possibly related to a video game. But the latest flurry of stories centre on a number of alleged violent crimes with links to the character.

Rico says all of this must fascinate someone, just not Rico...