THE first thing to know about Slender Man is that he is not real – though a great many people think he is. Slender Man is, to the world of living human beings, what fake news is to real reporting. This doesn’t mean that this strange, faceless figure - a modern bogeyman under the bed - hasn't had a significant impact on the world. He has - in fact, he lives inside the minds of millions of us across the world, particularly impressionable young teens.

The evolutionary scientist Richard Dawkins describes Slender Man as a meme, or viral idea, that has spread “exponentially” since the birth of the web. Others see him as an internet urban legend or a “fakelore” figure. Either way, he stands out from the crowd: preternaturally tall, suited, blank-faced, with long arms and, frequently, tentacles, often to be found lurking at the edges of children’s play areas or in woods. In the very first picture of him, photoshopped into existence in 2009, you can see him there, behind a crowd of children, just a blur of a face. Now he is ubiquitous, on every platform. It’s possible to find him in videogames, or as knitted versions on Etsy, or Halloween costumes. The Enderman character in Minecraft – really it’s another offshoot of Slender Man.

Slender Man is also the central figure in an attempted teen murder case that shocked America - and is now ready to come to court. To one of the accused, 12-year-old Morgan Geyser, Slender Man “is everywhere”. Geyser, chillingly, made the comment as part of her confession to the attempted murder of a schoolfriend in a Wisconsin park in 2014. In a planned act of violence, she, along with her friend and accomplice, Anissa Weier, attempted to murder Payton Leutner, also 12 years old, after spending a birthday sleepover with her. Their explanation was that they were doing this under the orders of Slender Man, to appease him, and gain a place with him at his mansions.

So, as you can see, while Slender Man may not be real, he has had a shocking impact on real word events. Partly that’s because people - perhaps tens of thousands of them - really believe in him. Crucially, these two girls believed in him. “If he’s stalking you,” said Geyser, in her confession, “you see him in your dreams.”

Slender man, therefore, in some figurative way, will go on trial with these two girls when they face adult court. Questions will be raised once more about what we can learn from this story. In a world where alternative facts and online echo chambers are an increasing concern, the role of the internet in this crime, and others seems acutely relevant. Over the past two years there have been reports of other alleged Slender Man inspired acts of violence, among them, a knife attack in Carolina, and a house-burning in Florida.

How did a fictional creation come to have such real world power? Slender Man wasn’t born all that long ago. He came into existence in 2009 when Eric Knudsen, under the pseudonym Victor Surge, posted a series of pictures on the website Something Awful as part of a photoshop contest to create something that would seem real. From there he spread to Youtube, and other platforms like 4chan’s paranormal board, then on to video games, horror stories on the Creepypasta site, “slenderotica”, and even a Church of the Slender Man that asserts his divinity - all of which goes to solidify the sense, for some, that he is real.

Digital folklorist, Trevor J Blank, one of the experts interviewed in a new documentary, Beware The Slenderman, describes him as “the modern day bogeyman”, onto whom a huge range of societal fears are projected. “Because it’s faceless, because it’s quiet, because it doesn’t speak words, it’s open to a lot of interpretations, a lot of projection. It varies from person to person as to what Slender Man is. He’s the creature who lives in my closet. He’s the guy in the windowless white van; the faceless stranger who kidnaps kids… Slender Man can be whomever you want him to be.”

The fact that we have a full account of Slender Man’s creation, however, doesn’t stop people from believing in his existence. It’s not difficult to find forums where people declare their belief in Slender Man. Comments like the following, on the social news aggregator Reddit: “I've seen him, I've dreamed about him, my ex-girlfriend and her little sister have both been haunted by him since before they knew what he was...So, I submit this comment at the risk of being ostracized for actually believing in an urban legend.”

As Aaron Sagers, an American pundit, observes, “a contingent of the paranormal community believes this creature actually exists - either as a manifestation of our collective thoughts, or that he has been always been present in our world.”

But since the attempted murder of Payton Leutner, Slender Man has gained an extra significance. The Beware The Slenderman documentary focused heavily on the role of technology and the fact that Weier and Geyser had come across Slender Man over the internet. Almost as sinister in the film as Slender Man are the repeated shots of tablets and Ipads. Director Irene Taylor Brodsky also highlighted the girls’ loneliness and mental illness. Geyser has been diagnosed with early onset schizophrenia, Weier with delusional disorder and schizotypy. It’s this collision between mental health and the complexities of the web that the documentary examines: how internet use may be making it more difficult for children to navigate the messy and blurred line between reality and fantasy.

Jacqueline Woolley, a psychologist interviewed, observes: “The concept of what’s real has always been pretty messy. Technology is creating these new situations in which it’s becoming even messier.”

Slender Man is a bogeyman figure that has taken on many meanings. He has become a vessel for our biggest fears. One of these is that the internet may be damaging not only our children, but all of us. This blank-faced figure in his business suit, could very well be a metaphor for the internet itself, reaching out with its tentacles, stealing away the children.