Stories that made Slender Man famous include the Marble Hornets Project and the work of Eric Knudsen. Based on Knudsen's altered photographs and fictional accounts, the character of Slender Man first appeared online in 2009 and quickly grew into a complex urban legend.
Slender Man is a fictional horror character usually depicted as a very tall, slim, faceless being in a black suit. The character first appeared in Eric Knudsen's edited photographs, which he posted on Something Awful's website in 2009. The photographs' popularity inspired Knudsen to elaborate on the character, creating the story of Slender Man's part in a 1986 library fire. Another Something Awful user later created the Marble Hornets Project, a series of online videos centered around Alex, a fictional character who encounters Slender Man.