The Slenderman

Slenderman was a popular internet legend created in June 2009. But when two 12-year-olds tried stabbing their friend to death, this mythical creature took on a life of its own.

At first, Slender Man was just an internet meme. But then, it became a frightening folktale whispered among American youths. And before long, the Slender Man legend inspired a few of these young people to kill.

But how did a fictional character created on the internet cause so much violence? And why did he become so popular in the first place? Let's take a look inside the real Slender Man story and where it all began.

On June 10, 2009, Slender Man was born out of a Photoshop contest on an internet forum. The challenge, which was posted on the comedy website Something Awful, encouraged people to take regular photographs and make them look scary by adding realistic ghosts, ghouls, or monsters.

Eric Knudsen, who went by the username Victor Surge, responded to the call by creating Slender Man. A ghostly figure with a featureless face, this character was creepy enough to make the photos go viral.

"It was pretty spontaneous," Knudsen told an interviewer in 2011. "I saw some of the pictures in the thread and just decided to make something that I myself would find creepy."

Inspired by the "surreal imaginings" of H.P. Lovecraft, Stephen King, William S. Burroughs, and a host of folklore creatures, Knudsen took some old black-and-white pictures of children playing and inserted a tall, thin, grainy figure in the background. In one image, he added tentacles to the figure's back.

One of his photos also featured a cryptic caption that added to its creepy allure. It read, "We didn't want to go, we didn't want to kill them, but its persistent silence and outstretched arms horrified and comforted us at the same time … 1983, photographer unknown, presumed dead."

Knudsen never could've imagined how many people would be inspired by his character - or that some would take their enthusiasm too far.

While Knudsen gave Slender Man his name and physique, the Slender Man legend was the communal, home-grown creation of a slew of internet users.

"If you want to study the life cycle of a meme from a random internet post to a fully realized, culturally known concept," noted Carli Velocci for The Verge, "you can't get much better than Slender Man."

On June 20, 2009, just 10 days after Knudsen's posts, the YouTube channel Marble Hornets premiered. The channel featured a Blair Witch Project-style found footage series about a film student being stalked by a figure known as "The Operator" - which appeared to have been inspired by Slender Man.

Produced by three film students from Alabama, Marble Hornets quickly began to garner fans on YouTube. Joseph DeLage, Tim Sutton, and Troy Wagner shot the nearly 90-episode series with practically no budget - and it ran for five years. And it still boasts more than 500,000 subscribers.

Other Slender Man-inspired videos and video games soon followed, appearing on websites with hundreds of thousands of visitors. In these depictions, Slender Man was always a tall, faceless figure with a dark suit and long arms, who usually had tentacles on his back. But fans soon filled in the blanks of the mythos with their own ideas as to what he did and why.

"The ‘open source' nature of it - a wide-ranging canon with lots of gaps to fill in around a fairly well-defined spine - helped a lot, I think," said Cat Vincent, a Slender Man enthusiast.

Users posited that he preyed on children, beckoning them into the woods and inviting them to kill in order to be initiated into his "proxy." His modes and motives were always left ambiguous. But in many ways, it was scarier not knowing any of the specific details about his backstory.

"Before you had angels and succubi, and then ghosts and spirits, today we have shadow people and inter-dimensional beings," said Knudsen. "The Slender Man, and other newly created entities, are just the newest addition in the progression of a long, and very real, human tradition."

Slender Man was a classic example of a "creepypasta" - a modern horror legend that makes the rounds on the internet after several people copy and paste it around the web. But many believe that this creepypasta reached its peak popularity in 2012. After that, it began to peter off.

What had once been the collective labor of love by a close-knit family of anonymous internet users soon became a commodity.

In 2013, the first-person horror video game, Slender: The Arrival, premiered as the commercial successor to the free-to-play indie game, Slender: The Eight Pages. The story of Slender Man was now for sale - tarnishing its home-grown appeal and disappointing many of its early fans.

But this disappointment was nothing compared to the real-life panic that ensued after a 2014 stabbing - which was inspired by Slender Man.

On May 30, 2014, three 12-year-old girls had a slumber party in Waukesha, Wisconsin, a suburb of Milwaukee. The next morning, one of the girls nearly bled to death after she was stabbed 19 times with a kitchen knife in the middle of the woods. Horrifically, her two "friends" that she'd spent the night with were the ones responsible for the brutal crime.

Bleeding from her arms, legs, and torso, Payton Leutner managed to drag herself to a path, where a cyclist found her and called 911.

This Haunted House of Horror is brought to you by Manimal and Heidi!