He initially appears as one of the missing actors from Alex's student film, Marble Hornets. However, because of a chain of events that occur later in the series, Tim eventually becomes the central point of view. Tim is well-noted for his sideburns, earning him the fan nicknames "Timburns" and "Suttonchops" (after his actor's surname), and for being one of the major driving plot devices in the series.
At different times, Tim seems to exhibit symptoms of The Sickness, as shown by his violent coughing fits. While Tim does smoke, the idea of him suffering from smoker's cough may not be true as the concept of "The Sickness" was created from things like Jay, Tim and Brian's coughing and coughing up blood throughout the series.
Tim makes a few cameo appearances in the follow-up series ‘Clear Lakes 44’. It is unknown when the footage of him takes place. At one point he gives a box to what appears to be ”Birdwatcher”, the main character of that series.
The Masked Man, also known to fans as "Masky", is an antagonist in Marble Hornets. At first, it was unknown which side he was on, as he attacks Brian and Alex multiple times, and was initially thought to have been a minion or servant of The Operator, and the actions surrounding him have lead to the concept of proxies being created, although Masky himself (nor Hoody) has never been stated to be a proxy.
However, it is worth noting that the Masked Man actively works against The Operator meaning he would usually not be considered a proxy. The Masked Man was generally regarded as a mysterious antagonist; however, his actions in saving Jay and Jessica from being murdered by Alex in Entry #52 suggested otherwise.
The Masked Man first appears in Entry #18, sitting in Brian's house, in which he rushes at Jay. He continues to antagonize Jay, and it is revealed in Entry#35 that Tim is the Masked Man. It is unknown why Tim has taken on this role.
Speculation holds that he is, or is/was part of, totheark, as he appears in several of the videos. ((He is totheark discovered and confirmed))
In Entry #66, Tim and Jay visit an abandoned hospital, and he brings Jay to "his room." Tim reveals that he was a patient at the hospital since he was very young and he had "hallucinations" that he could not remember. He says he was worried that these hallucinations were actually The Operator and that everything (Alex, Jay, and the others being stalked by the Operator) was his fault.
This has been confirmed by the creators.