Canon History and Information (part 1)

For any Non canon abilities and descriptions, please see Unconfirmed Slenderman Assumptions

Slenderman has no exactly defined or specified history, however contributors have placed early sightings of Slenderman-like beings in early 1600s Germany and before, where it took the dress of a knight or royal figure. Germanic fairy tales and mythology also makes use of the creatures to be used as cautionary tales for children.

Photographs from the early 1900s were the next confirmed reports, where imagery of Slenderman can be found in classical black and white and sepia imagery. Reports from this time indicate sightings in America, the UK, and Russia, as well as reports of child disappearances.

By the mid-1900s, some rare run-ins occurred in the war zones in Germany, apparently Slenderman's native land. Soldiers were the primary targets here. In America and Canada, reports of missing skiers and children appeared, coming from forested areas of the nations.

After a spree of building burnings from unknown causes, several deaths and a few surviving witnesses, it could be gathered that the Slenderman had the following traits:

Slenderman will find interest in a victim for reasons unknown
It would then contact the victim, if it is a child, presenting itself as friendly
The adults he stalks have a common trait: they have all been through a terrible tragedy in their life, even if the tragedy was made by Slenderman directly
If an adult, it would stalk the victim for long amounts of time causing what is known as "Slender sickness" causing massive paranoia, nose bleeds, nightmares, hallucinations appearing to only the sick person, and many other dangerous symptoms.
Eventually, it would abduct the victim into nearby forest, where they would be killed.
In 'messy' cases, it may remove evidence of its existence by causing fire of their home, place of work, or school
Death of the victim originally occurred through an odd means- the victim would be impaled on branches of very tall trees while still alive, and bleed to death. The organs would be individually removed, then placed in plastic bags. They would then be replaced into the body in their original positions, plus the plastic bags. The victims' corpses do not show any sign of a struggle. As time has gone on, this practice has seemingly been abandoned.
In the late 1990s, technology shed more light on the creature through the use of commonplace cameras and camcorders. Slenderman was recorded and photographed stalking potential victims many times.

In the late 2000s to early 2010s, several individuals recorded ongoing stalking and attack scenarios of themselves and their friends. These video accounts are codenamed Marble Hornets, EverymanHYBRID, DarkHarvest00, MLAndersen0, and TribeTwelve. As well as certain Rivn videos.

The new foray into Slender Man's powers, abilities, and attacks have shown drastic difference from his original behaviors. The original desire to impale targets on trees, his rather aggressive attitude, and attacking mainly children have been altered. It appears he seems to enjoy targeting humans who have seen him in childhood and following them for years. He appears to do so in such a way that the target is unaware of his presence for potentially months, years, or even decades, and typically won't be aware at any point in time until it is far too late.

His behavior is extremely passive aggressive, where he stalks, follows, and torments an individual by repeatedly showing his presence. He will typically do so in invasive ways, such as appearing inside someone's house, outside their home, on roads they travel, at their place of work when they are alone, or while the target is sleeping. This will create a general unease of the target, as the invasion of an entity in their own safety zone will begin sparking incredible paranoia. Most often he won't attack the target for extended periods, instead just following the target and tormenting them. This period can last anywhere from several minutes to years.