Marble Hornets is a found-footage web series begun on YouTube by Troy Wagner and Joseph DeLage on June 20, 2009 — ten days after Slender Man was created. Jay digs into the truth of why his friend Alex Kralie abandoned the student film "Marble Hornets," and comes face to face with the being called the Operator (Slender Man within the story). Ninety-two episodes ran on the main channel alone.
The heart of this work is the invention of a form. A narrative structure using seemingly amateur footage and a separate side channel established the template for ARG horror that bleeds past the screen into reality. It left a direct mark on successors like EverymanHYBRID and TribeTwelve and on the whole YouTube horror renaissance.