Xavier Remington 
Several thousands of years ago the infamous immortal shape-shifting mind control master Slender Man was banished to Earth as an eternal prison sentence by his own people from another dimension. Almost immediately he was worshiped as a God by a small group of Egyptians he encountered in the Sahara Desert. They called him the Faceless God Of The Sands. He attempted to communicate with them telepathically but ended up driving half of them instantly mad. Most committed suicide within a day! Clearly he’s honed his telepathic human brain interface skills since then. These psychic skills enabled him to create his infamous Slender Proxies. Those who commit murder for him as he is bound by otherworldly forces to not do so directly except in cases of self-defense. His helpless proxies eventually went insane from the Slender Sickness after a period of time before finally committing suicide. The Slender Sickness is an advanced form of paranormal psychosis caused by prolonged psychic communication with Slenderman. There is no known cure.
Subsequent Slender Man cults would form over the centuries, and Slender always ended up inadvertently eradicating them indirectly via the sinister Slender Sickness. It seems he can technically kill humans directly if it’s inadvertent, or in defense of himself. Powerful practitioners of dark magic looked to form a cult around him, and tap into his unique parallel dimensional power. They were the ones who would be able to best withstand contact with Slender, and not acquire the Sickness. Regrettably for them they found their magic would become chaotic, and unpredictable when communicating with him for too long. They may not have gone mad but some were never able to practice magic again. Inevitably they had no real allegiance to Slender, and abandoned him when they couldn’t exploit his powers. Clearly his metaphysical energy force was completely incompatible with all forms of magic known in our dimension. Except of course the magical innocence present in kids that Slender Man feeds off of. Some have even indicated that magic as we know it most likely doesn’t even exist in his home dimension to begin with.
Slenderman Finds Teens To Be His Salvation
These teenagers, generally in the 13-16 age range, became the core of his infamous Slenderman Cult. Those who serve him exceptionally well get the gift of immortality via the extension of his personal psychic aura within their own spiritual energy auras. These misguided teens serve a number of functions. Primarily to guard Slenderman’s kidnapped kids at various hidden locations on Earth, and act as backup should someone manage to overtake him. They must be at his planned locations in advance which is why he had cultists all around the world. He may be able to teleport anywhere on Earth instantly but it does drain his energy. It’s thought that even teleporting one other person exponentially reduces his power. Certainly in the case of the 2015 Halloween Slender Man Plot it made sense to have teen cult in the Kansas town where he spent two months working his wayward mesmerization.
There are several small cults Slender keeps at various locations around the world. 
