by whom was it developed?
Eric Knudsen
Slender Man
The Slender Man (also spelled Slenderman) is a fictional supernatural character that originated as a creepypasta Internet meme created by Something Awful forums user Eric Knudsen (also known as "Victor Surge") in 2009. He is depicted as a thin, unnaturally tall humanoid with a featureless head and face, wearing a black suit.
when did slender man the movie come out August 10, 2018 was the movie based on any incident? No - Slender Man  is a fictional supernatural character could you please describe him? Thin, tall humanoid with a featureless head and face, wearing a black suit.
wiki:18541221
Slender Man [SEP] Introduction
The Slender Man (also spelled Slenderman) is a fictional supernatural character that originated as a creepypasta Internet meme created by Something Awful forums user Eric Knudsen (also known as "Victor Surge") in 2009. He is depicted as a thin, unnaturally tall humanoid with a featureless head and 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, typically composed online. Fiction relating to the Slender Man encompasses many media, including literature, art and video series such as "Marble Hornets", wherein he is known as The Operator.