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Jay Merrick was the main protagonist of the Marble Hornets ARG and the central point of view for most the series until his disappearance in Entry #80 and Entry #83 where his death was confirmed.
J (revealed on his twitter to be short for Jay) is the owner of the Marble Hornets 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 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.
Originally brought in as the main cameraman for Marble Hornets, he began to catalog the strange occurrences, notably Alex and his mental breakdown. After watching the tapes that showed the odd events, Jay continued searching for answers, leading to several sights and encounters with an individual known as The Operator and various people caught in its existence.
During Entry #83 Tim's search for Jay finally comes to an end as he encounters Jay, now dead with a bullet wound as he was teleported to various locations. His body was surrounded by pieces of paper with the Operator symbol on them, and a note that read "YOUR FAULT". Assuming Hoody to be responsible, Tim goes after him to get revenge for Jay's murder.
In Entry #86 Tim confronts and kills Alex using Jay's camera and knife, symbolically completing Jay's mission and avenging his death.
In Entry #87 Tim lies to a still alive Jessica that Jay had moved away and wanted to start his life again somewhere new.