The Slender Man

 The Slender Man (also known as Slenderman) is a fictional character that originated as an Internet meme created by Something Awful forums user Eric Knudsen (a.k.a. "Victor Surge") in 2009. It is depicted as resembling a thin, unnaturally tall man with a blank and usually featureless face, wearing a black suit. Stories of the Slender Man commonly feature him stalking, abducting, or traumatizing people, particularly children.
The Slender Man is not confined to a single narrative, but appears in many disparate works of fiction, mostly composed online.

 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. Although previous entries had consisted solely of photographs, 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":
The quote under the first photograph 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.

The quote under the second photograph read:

One of two recovered photographs from the Stirling City Library blaze. Notable for being taken the day which fourteen children vanished and for what is referred to as “The Slender Man”. Deformities cited as film defects by officials. Fire at library occurred one week later. Actual photograph confiscated as evidence.

— 1986, photographer: Mary Thomas, missing since June 13th, 1986.

The Documentary of Slender Man: