Tim, with the Operator standing behind him through the window.
Tim is one of the actors from Marble Hornets. He seems to have been one of Brian's closest friends, and by extension also a good friend of Sarah's. He is first mentioned in Entry 5, and appears in Entry 9, Entry 15, Entry 17, Entry 20. In the archival footage that Alex Kralie gave to Jay, Tim showed signs of the health problems (e.g. coughing, headaches). He is also seen taking some white pills in Entry 16.
Interactions with Jay
Warning: Major plot twists and reveals under spoiler tags.
Tim is first mentioned in Entry 5, while Alex and Jay are doing some location scouting.
He is first seen in Entry 9. He is trying to film a scene with fellow actress Sarah, but it get more and more difficult due to Alex behaviour.
It's named at the end of Entry 12, noting he has just arrived.
In Entry 15, three years after Marble Hornets' filming, Jay contacts Tim and arranges an interview, claiming to wanting to finish the movie. Instead, he begins to ask Tim about Alex and the circumstances surrounding the shooting. Tim divulges little information, though he explained that he was Brian's friend and next-door neighbor, and that he didn't know Alex very well (although Alex and Brian were close friends).
He is not seen again untill Entry 52. Jay casualy finds him coming out of some place, lighting a smoke.
In Entry 53, Jay approaches him using once again the excuse he used back in Entry 15.
It could be that the pills Tim can be seen taking pills in Entry 16 as stated above, which Jay finds in The House in Entry 16 and examines in Entry 19.5. These could be Painkillers, or some other form of drug, to try and help take his mind off things, perhaps because he was being stalked by the Operator. But I think it is much more likely that he was simply taking Pain Killers to help him from the pain that the Operator's pressense causes. I don't know whether I personally believe this or not, but it's certainly a possibility. -Moooo4me
It's possible that Tim may have more to do with encounters with the Operator than we thought. In Entry 55 he mentions he's had a history of headaches and paranoia. At the time of this shoot, it doesn't appear that enough time would have passed from the beginning of the Marble Hornets project for his symptoms to be considered history. It seems more likely that he's had encounters before the filming began. Also, he is the one who suggests the abandoned building to be used for the schoolhouse setting. It was he who led Alex there, not the other way around. ~NeoCloud
Entry 60.5 confirms that Tim has been experiencing slendersickness since at least the mid 90s and was treated at the facility that is now the burned out building that he is so apprehensive about returning to. This was many years before Marble Hornets began filming. Tim is one of if not the first person involved with Marble Hornets to encounter the Operator.
enttry 37 Shows Alex at his birthday party on April 4, 1991. When he blows out the candles, the operator appears in the video. Whether he was actually present or just superimposed into the video is a matter of debate. One of the other children may have been Tim. This could imply that Tim and Alex knew each other longer than they remember. Amnesia from the Operator could explain why they don't consciously remember each other before they met for Marble Hornets.
In enttry 37 Alex was most likely 5 or 6. He was born in 1982, 1983, or 1984 then. According to Tim's medical records, he was born around 1986 or 1987. If he was at Alex's birthday party, he would have been much younger than Alex. Not to mention that neither Tim or Alex lived where Marble Hornets was filmed at that time. (The original Something Awful thread says that Alex was 8 when he moved to that area, and Tim most likely lived near Rosswood) ~ Kaylee2014
Tim is seen taking pills a number of times in the series, from season 1 when they are found in the abandoned house onwards. In the medical forms found in Entry 60.5, there is a part where anticonvulsants are referred to as a preventative measure. The pills Tim is seen taking throughout the series could easily be these same anticonvulsant medications.
One of the functions of an anticonvulsant is to "suppress the rapid and excessive firing of neurons that start a seizure" (taken from wikipedia). Neurons firing are electrical activity. The Operator has some sort of undefined effect on electrical systems, and this could easily include peoples' brains. This could mean that, while Tim is taking anticonvulsants, he is not effected by the Operator in the same way as other people are. This could include a decrease in things like memory loss and disorientation.
There is evidence from the first season that Tim was taking the pills for seizures then — Jay steals his pills, and the next time they meet Tim has an apparent seizure, and the pills get stolen back — and this is the first time specifically that we see him taking pills in the current day. In this case the pills would in fact enable Tim to be Masky but not require it, and would mean that Tim's ability to be Masky is an act of his own agency.
Tim, when on his medication, could be keeping his memory far more than your average slender-stalkee, which could itself account for the 'Masky' behavior. Rather than an alternate personality, the mask is a way from keeping the Operator from specifically recognizing Tim when Tim decides to do stuff that he's learned (over many years, apparently, of being involved in these shenanigans) agitate the Operator — ie, being on camera, taping TO, getting involved with people who are being stalked by TO.
The continued knowledge of an eldritch horror hanging around would wear on a guy, though. Two theories: Tim could have at some point decided seizures were less dangerous than continued knowledge of TO, and stopped talking his pills in order to let his memory be wiped like everyone else's before resuming his medication, or Tim could have put away the mask and distanced himself from all things Marble Hornets intentionally while still taking his pills and retaining the memories.
tl&dr; Tim takes anticonvulsants for a preexisting condition, and the anticonvuslants themselves contribute to his ability to don the mask but don't require it.