The Slender Man is undeniably the most famous of all the Fears, and by far the most prolific in its hunting of Runners. It has a realm, known as the Path of
2571984-Slender Man 9

The Slender Man, drawn by a Runner

Black Leaves, which appears as a massive forest of endless birch trees with black leaves. Azoth lays in pools and rivers in this path.

The Slender Man is known for its brutal, sadistic methods (covered later) and its disturbing appearance. The Slender Man is by far the most distinctive of all Fears, with tendrils that either extend from its back, or rail off of its arms in place of hands. Its head is a blank, white, orb with the outline of a face, depressions were the mouth, nose, and eyes would be. It is constantly seen in a black suit, with a red or black tie (reports seem to indicate the tie changes colors at will) and a white shirt. The Slender Man is sometimes seen taking the form of a massive tree with black bark, knotted and twisted. The Slender Man’s servants are known as Proxies, and he takes servants forcefully, with few willingly becoming Proxies. These Runners suffer from Slender Sickness (though most Fears cause this, the Slender Man has been associated with it) for periods of several weeks to several years until their will breaks. At this point the Slender Man may induct them into Proxyhood or kill them.

The Slender Man’s methods of killing is likely the reason it has become so famous and internationally known. The Slender Man often tortures its victims, flaying them alive or impaling them, often removing the organs of the victim. The victim’s bodies are often left in forests or burned in the place they were slain (though the latter is more likely if the killing takes place in a building).

The Slender Man has been known since the times of the ancients, with multi-limbed beings chasing humans appearing as far back as cave paintings. Carvings in Germany tell of Der Ritter, or "The Knight", a multi-limbed entity who slays all who come near it.