The main protagonist of the series, who runs the MarbleHornets YouTube channel. As he is the one filming most videos uploaded to the channel, he is rarely seen on camera. He and Alex Kralie were once friends who worked on Alex's student film together, but the two fell out of contact after production on the film was cancelled. Jay later began uploading Alex's taped footage to the internet, setting off a chain of events that resulted in him becoming a target of the Operator.
Approximately three years before the series began, Alex attempted to direct a student film titled "Marble Hornets". During his time on the set, Alex began encountering the Operator and his mental state began to deteriorate, with him beginning to act rudely toward his actors and assistants over time. Alex later handed the production footage he had filmed over to Jay, although he had initially wished to burn it. Sometime later, he and Jay fell out of contact.
An acquaintance of Alex who worked on his student film as an actor. Tim was later interviewed by Jay, who had also helped with the movie's production. He is known to have a history of medical conditions. It is revealed that Tim is actually masky, an individual known to have attacked Jay many times.
A mysterious girl who Jay encountered at a hotel. He later learned that she was suffering from amnesia, much like himself. When Jay reviewed the tapes he had filmed over the previous seven months, he learned that the two had met before and that she had once been the roommate of Amy, Alex's girlfriend.
Brian was one of the main actors in Alex's student film. Jay first encountered the masked man in what he believed to be a burned down hospital and then chased him into a maintenance tunnel but then stopped due to the darkness of the tunnel.
Seth worked on Alex's student film as the cameraman. Little is known about him. He seemingly died, or was “Left behind“ for he was not seen from again after Alex and him went to the tower earlier.
Sarah was an actress in Alex's student film. Little is known about her, although she seemingly did not think highly of Alex toward the end of production on the film.
Amy was Alex's girlfriend after he lost contact with Jay as well as Jessica's roommate. She went missing after the Operator appeared in Alex's house around the same time that Jay was investigating him. What became of her after her disappearance is unknown.
The name of a YouTube channel that has some sort of connection to the Operator. Several face-concealing characters have appeared throughout the series who this name may be attributed to, the most notable being a masked man and an individual wearing a hood.
A mysterious entity with undefined abilities. For unknown reasons, he has seemingly had an interest in Tim Wright since he was a child. While Alex was attempting to direct his student film, the Operator drove him and several of his colleagues to the point of near-insanity. When Jay later began investigating Marble Hornets, the Operator seemingly turned his sights on him as well.
The "individual l wearing a hood" from "Totheark". His identity has been confirmed as Brian, revealed by Alex after his death. It is up for debate whether or not he's working for The Operator.