The Slender Man is a fictional character that originated as an Internet meme in 2009.

He is commonly described as very tall and thin with unnaturally long, tentacle-like arms (or merely tentacles),which he can extend to intimidate or capture prey. He has a white, featureless head and appears to be wearing a dark suit and tie.

The Slender Man is associated with the forest and has the ability to teleport. Proximity to the Slender Man is often said to trigger a “Slender sickness”; a rapid onset of paranoia, nightmares and delusions accompanied by nosebleeds.

The Slender Man was created on a thread in the Something Awful Internet forum begun on June 8, 2009, with the goal of editing photographs to contain supernatural entities.

On June 10, a forum poster with the user name “Victor Surge” contributed two black and white images of groups of children, to which he added a tall, thin spectral figure wearing a black suit.

Surge supplemented his submission with snatches of text, supposedly from witnesses, describing the abductions of the groups of children, and giving the character the name, “The Slender Man”.

On May 31, 2014, two 12-year-old girls in Waukesha, Wisconsin allegedly held down and stabbed a 12-year-old classmate 19 times.

[W]hen questioned later by authorities, they reportedly claimed that they wished to commit a murder as a first step to becoming “proxies” (acolytes) of the Slender Man.

One of the girls, Weier, expressed remorse. Kind of. “The bad part of me wanted her to die, the good part of me wanted her to live”.

Geyser, on the other hand, told police, “It was weird that I didn’t feel remorse,” noting as well that what she did was “probably wrong”.

Right. Probably.

Exhibit A: Clinical Psychopath in the Form of a 12-year Old Girl.

According to RT:

[C]ourt documents said, “Weir stated that many people do not believe [Slender Man] is real and she stated she wanted to prove the skeptics wrong”.

Originally the plan was “to put duct tape over P.L.’s mouth, stab her in the neck, put the covers over her to make it look like she was sleeping and run”. But the plan changed that night, and the two Slender Man devotees decided to kill the third girl the next morning in a park bathroom, where there was a floor drain “for the blood to go down,” and then “stabby, stab stab,” Geyser later told police.

But once they got to the bathroom, Geyser handed Weier the knife but the girl couldn’t go through with it and asked the birthday girl to do it.

So then the girls decided to try the woods, where they played hide-and-seek. Weier told P.L where to hide and that she should lay face down in the dirt. When the victim refused Weier sat on her, and she began screaming.

The two perpetrators began secretly debating who would do the restraining and who would do the stabbing, they told police. Eventually they decided Geyser would wield the weapon, but not until Weier told her to.

When Weier told her “kitty, now”, Geyser responded, “Don’t worry, I’m just a little kitty cat”.

Via Wikipedia.