J (revealed on his twitter to be short for Jay) is the owner of the MarbleHornets YouTube account, and the uploader of The Entries. He is able to be contacted through his Youtube account and through his Twitter account.
Jay was, 3 years ago, a college friend of Alex Kralie's. He assisted Alex in doing production work on Alex's film, Marble Hornets, with location scouting and the like. When he head that Alex had dropped the Marble Hornets project, he asked Alex what he planned to do with the tapes. Alex replied "burn them."
Hating to see such work go to waste, Jay coerced Alex into giving him the tapes. Alex handed them over after giving the condition that Jay was never to mention them to Alex again. The tapes went to Jay's closet and were subsequently forgotten, to be found three years later. Now curious as to what he would find that drove Alex crazy and caused him to cancel his project, Jay has begun systematically working through watching them all. Anything he finds of interest he is uploading to youtube as The Entries.
Jay originally posted his videos to the Create Paranormal Images thread on Something Awful, but has since moved to Twitter as his medium.
It has been revealed in recent Entries that Jay is missing large sections of time, from the period between Season 1 and 2, and possibly large periods during the original filming of Marble Hornets.
HyenaGod to Jay on November 11, 2009
hey, I was wondering since your knife is missing in entry 18, did you stab that masked person you caught on film?
Jay to HyenaGod on November 28, 2009
Not sure, but I doubt it. -J.
Ongoing Health Concerns
According to his Twitter account, Jay's health has been declining since he started reviewing the Marble Hornets tapes. He seems to be suffering from a variety of symptoms:
Finding it harder to sleep lately.
Very sick. 104 fever. Need to sleep instead of looking through the tapes.
Been sick for the past week.
Headache. Need to lay down for a while.
Blacked out last night. Going to the doctor tomorrow.
During a string of Twitter updates on March 22, 2011 after Jay found something that troubled him greatly and attempted (unsuccessfully) to log into his YouTube account, he again brought up signs of his deteriorating health.
I have the worst hheadache right now..
Keep thnking I'm hearing things.
Jay as an Unreliable Narrator
Jay's credibility as a narrator is in question to some degree.
The existing body of information on the subject of Alex is a massive unsorted collection of video tapes. A single person reviewing this collection out of order would have trouble understand the whole story. Any analysis Jay may make on the content of the tapes (via captions) may be inaccurate.
In addition, starting with Entry 17, there are several instances of Jay having large gaps in his memory. He does not remember the events shown in Entry 17, and he has no memory of what happened after the camera stopped recording him in both Entry 18 and Entry 19. Entry 19 also revealed that Jay had kept the information that he was taping himself from the audience for about a month. While Jay does not seem to have the intention to mislead, he is often missing information, or does not realize information may be relevant. Jay's memory seems to be having more and more gaps as time goes along.
YouTube user totheark believes Jay cannot be trusted because he is human.