The Slender Man is unnaturally tall. A dark-suited nemesis, a sinister stealer of children, he is sometimes described as having black tendrils that extend from his back, but always as having a white, eerie blankness instead of a face. He is said to have the ability to control mind and memory.

And he is not real.



But according to police, on Saturday two 12-year-old girls lured another girl to a forest in Wakuesha, Wisconsin and stabbed her 19 times. One of the girls allegedly told police they stabbed their friend to “prove [themselves] worthy to the Slender.”



Chelsi Tristan, a self-described insomniac from Raymondville, Texas, is working on a movie script about Slender Man, and said the character was particularly compelling to her because he reminded her of stories she heard as a child of La Lorona and La Cucuy, ghost-monsters of Hispanic legend. She was, she says, sickened by the Wisconsin attack.



“As a writer of the Slenderverse series, I didn’t know how to respond," she told the Guardian. "I was thinking: how could this happen? How could these kids feel that?” She said she was scared people would blame literature like hers for the way people wrongly blamed the music of Marilyn Manson for the shootings at Columbine.



The monster that was allegedly the reason for the brutal attack in Wisconsin had captured Tristan’s imagination, along with that of hundreds if not thousands of other writers, artists, and filmmakers. His origin is surprisingly humble, however; it lies not in pre-history, or Norse or Greek legend, but the message-board community of a site called SomethingAwful.com, where he was created just five years ago.



'He managed to look like a predator and a man, all at the same time'

The first photograph of Slender Man is old, black-and-white and smudged with age. The caption underneath it says that it is “one of two recovered photographs from the Stirling City Library blaze.” In the foreground, a child smiles at the camera from the steps of a playground slide. Other children play nearby in the shade of some trees.



It takes you a little while to see it, in the middle distance, darkened in shadow under a tree. The figure of a man, but somehow wrong; unnaturally elongated and tall. If you peer closely, you can see shapes, like tentacles, behind him.



The picture was created using Photoshop on 10 June 2009 by Eric Knudsen, who went by the username “Victor Surge”. It was part of a competition to “create a paranormal image” on the message-boards of SomethingAwful.com.



“The first couple pages of the "Create a Paranormal" image were pretty crappy,” said Drew Slater, who told the Guardian that he was on the message board that day. “Just some sort of ghost pictures lazily photoshopped. One or two were neat, I suppose, but a majority of them were uninspired.”



“Slender Man was different,” said Slater. “As you focused on him, you began to realize how ... wrong he looked. He managed to actually look like a predator and a man, all at the same time. It was spooky.”



The first photograph of Slender Man, created by Eric Knudsen in 2009. Photograph: Eric Knudsen Photograph: City of Stirling

“There was this magical moment a few days into the thread,” Andrew Peck, a PhD candidate in folklore and media at the University of Wisconsin who has also been involved with Slender Man from the beginning, told the Guardian. “People began riffing on it, took this character who is not well defined and made it their own.”



“That's part of the fun of the phenomenon for many of us,” said a fan who gave her name as Larke, who wrote a short story placing Slender Man in the era of Arthurian legend. “We know it's not real, so we can create our own history around it to make it more authentic-feeling, and more creepy for people who engage themselves in the lore.”



The character of Slender Man embodied a primal, archetypal horror that the members of the forums found compelling. Within days, there were the beginnings of a Slender Man canon of pseudo-mythological literature. Those within this community call it either the “Slenderverse,” or, simply, “the mythos.”



Users wrote stories, doctored pictures, created elaborately faked historical artefacts. Within a month, a filmmaker had begun a found-footage style series on YouTube called Marble Hornets, which to date has 380,114 subscribers and more than 73m views.



A spooky figure 'bleeding over into our reality'



It quickly became part of an online literary genre called “creepypasta,” a word whose etymology lies in “copy-paste” – literally, stories to be duplicated and shared online. The genre originated on Something Awful and the boisterous message-board 4Chan, but has its own site and wiki where writers shared their stories. Creepypasta, as opposed to copypasta – the generic term for shared written content – was especially for horror stories.



Slender Man – referred to fondly as “Slendy” by those in the know – quickly became one of its most popular tropes, with thousands of stories, artworks, YouTube creations and even a series of video games created around it.



Dr Eric Newsom researches creative communities in digital spaces at the University of Central Missouri, and has studied Slender Man. He said community members would suspend disbelief, talking as if Slender Man was real, enjoying being scared by this sinister figure together. On other boards, he said, they would talk in meta-storytelling terms about how to craft the character.



But how did a mythological demon, born as a hoax and grown as a crowd-sourced literary character, end up apparently involved in a real-life murder attempt?



The nature of this genre complicates that question. Cat Vincent, a journalist for the British paranormal magazine Fortean Times who has written extensively about Slender Man, said that “very early on, it was said that people are going to look at this and think it’s real.”



Integral to the Slender Man mythos, Vincent told the Guardian, is the Buddhist concept of “Tulpa” – a figure which is conjured into being through belief or thought alone. The Creepypasta community had tried so hard to build this character, bring him to life by the power of imagination. Had they, in a twisted way, succeeded?



Newsom, too, mentioned the concept of Tulpa. “The idea is,” he said, “it’s bleeding over into our reality.” It is an interesting idea – that like Shelley’s Frankenstein, the creepypasta community had summoned forth a demon they could not control, that it had bled into reality so much that he was now attacking people for real.



But Anthony Tobia, an associate professor of psychiatry at Rutgers University, was unequivocal in saying that you could not scapegoat Slender Man in this way. “Absolutely not.”



He thought it likely, if the allegations against them prove true, that the girls were suffering from a “shared psychotic disorder,” but cautioned that there were many questions as yet unanswered. “Were these two girls the victim of bullying,” he wanted to know. “At some point they lost touch with reality – what was their self esteem like? Was it weak enough that they might have been influenced by an outside source? Was one of the girls the leader, and one the follower?”



In a statement to the media, Slender Man creator Knudsen said: “I am deeply saddened by the tragedy in Wisconsin and my heart goes out to the families of those affected by this terrible act.”



The Waukesha school district has now banned CreepyPasta and other websites involving Slender Man. This worries members of the community, who fear a backlash. “Slender Man has provided a rich creative outlet for thousands, bringing people together as communities inspired to tell stories in unique ways,” said Newsom. “It would be a shame to lose that.”



Tristan agrees. “I don’t want [other writers] to stop because of what happened. I think the strongest thing we can do as a community is to keep going on,” she said.



She paused for a long time. “I don’t want this to come off the wrong way. I feel really, really bad for this poor girl. But I want to keep writing - I really enjoy writing about the Slender Man universe,” she said.



“It’s something that I love.”