"I don't think I'm being haunted by the more physically active version of Bigfoot. I don't think so."
The Slender Man, the White King, or a variety of other aliases was first recorded on Something Awful's Paranormal Images thread, by Something Awful user Victor Surge. He serves as the primary antagonist to CaughtNotSleeping. His motivations are as of yet unclear.
Behavior and Physical Properties
Slender Man in classic lore, stalks victims for unclear reasons. His origin itself is also unknown, other than the fact that he is not human, though he tries to appear as such. The Slender Man appears unnaturally tall and thin, wearing a black suit and tie. Though he tries to approximate human appearance, he is clearly otherworldly given his dimension and lack of recognizable face. It is not clear if the Slender Man requires any sustenance to survive, if he eat, drinks or breathes; nor if he perceives the world in the same that we do (i.e. if he can see or hear). However he can obviously sense his environment, often being found in wooded areas or in pursuit of his victims. He does not seem to speak of make any sort of noise.
The Slender Man seems to be able to bend the laws of physics, given his ability to move from place to place impossibly fast. Though it is suggested that this ability is disrupted when he is being observed, as he often moves stiffly and slowly on film. His presence does tend to disrupt camera function and sound, perhaps to allow him moments to travel unobserved. His presence has also been known to cause physical symptoms in his victims, such as coughing, paranoia, memory loss, and in the case of Caught, sleeplessness. Rarely presenting a real physical danger, Slender Man seems to stalk his victims until his aura causes them to go insane. If this is purposeful or not is, again, unclear. It has been theorized that The Slender Man has no interest in killing Caught but perhaps instead punishing him for some unremembered indiscretion. He has shown himself to be capable of physical violence towards the protagonists, such as in "26 2326916 1115262422" but Caught has also been successful in warding him off with a variety of methods, most notably a small jar of liquid given to him by 1AmTheHelp3r. The aura The Slender Man puts off has been said to be less present around Caught's Apartment.
The Slender Man has been know to take "Proxies", or people who are used for his own purposes, often functioning as his mouthpiece or a more physical threat. Proxies seem to be made of of people who have fully fallen to Slender Man's presence or have allowed themselves to become servants. Either RoivasSevil or 1AmTheHelp3r, or both, could be Proxy servants to the Slender Man; though 1AmTheHelp3r has previously stated that "There are no proxies only people with purposes".
It has been suggested by the evidence of other victims, such as those in the Runner's Journal, that there are other methods of dealing with Slender Man beyond the compulsive filming that most victims exhibit. In the Runner's Journal, the three victims attempt to keep Slender Man away using constant sound.
21129 21269 922518224 ~ The Slender Man appears at least twice in this entry. First far in the distance when Caught drops the camera, and then right behind Caught when he turns away from the bloody 20 dollar bill.
Sorry. ~ Caught reveals his previous encounters with The Slender Man. He plays a single encounter wherein Slender man can be seen inside his building, and again outside as Caught walks around his premises.
The sink. ~ After the hair doll appears the camera seems to flash back to Caught's first encounter with The Slender Man in the alleyway.
A brand new day ~ Slender Man appears and disappears multiple times in the background as Caught digs up the coffin left for him by 1AmTheHelp3r.
1472 Lansing Place Three ~ The Slender Man walks past the door as 1AmTheHelp3r fights with Caught.
1472 Lansing Place Five ~ After entering the woods Caught is chased by the Slender Man.
26 2326916 1115262422 ~ Caught is lured into the woods and beaten severely by The Slender Man
Rule 6 ~ After months of unconsciousness, 1AmTheHelp3r revives Caught. After a close encounter with the Slender Man, they flee, closely pursued.