Note: This version of Slenderman follows the Mansion AU and will share some headcanon stuff about that too since it's relevant.
•Slenderman is the oldest brother out of the 4.
•His mansion is a sentient being that feeds off of the negative energy which is why he has so many killers as residents. This benefits him because the residents go out to commit their crimes and come back to his mansion, allowing his sickness to spread throughout the cities and countries, keeping him powerful without having to do much.
•His mansion exists on another plane/dimension where time is stunted, this dimension is called the Ark, humans don't last long in there as their brains slowly break, the Ark only exists as long as he exists which is why he is so hell bent on having victims and spreading his "influence". Without his "influence" the Ark becomes unstable and is at risk of collapsing. Without victims he would become weak and eventually the Ark would fizzle out and everything inside would die.
•Slenderman used to be rather fatherly towards the residents but over the years he went back to being this cold, emotionally unavailable thing. This is because of built up stress he accumulated while trying to keep this symbiotic system between him and the Ark working. He fears death.
•Slenderman is very territorial, not just anyone is allowed to enter the Ark. Which is why he can get violent. To keep this control, he places pages around the Ark's forests for people to collect, if either him or his proxy's catch the person, they will be killed off. However if they get all the pages without being caught, they will either be allowed to escape or be turned into a proxy if Slenderman sees potential.
•There are multiple portals/entrances to the Ark, the most used one is the tunnel shown in Marble Hornets. The entrances are usually found down long corridors, under abandoned bridges, in basements, etc. Just places that humans don't normally go unless their trying to hide a body pretty much. They are also found in multiple countries, there is no limited range to the Ark's entrances.
•His sickness causes hallucinations, dizziness, headaches, paranoia, voices in the head, blood to randomly excrete from the nose, eyes, ears and mouth. The sickness effects every individual differently and the sickness does NOT mean you are going to become a proxy, sometimes its used defensively but all the uses for it always benefit Slenderman.
•He only cooks dinners for the mansion and most times there's usually residents going hungry without supper, so they have to leave to a nearby city or make their own food. However rat problems have in fact happened before which pisses him off so usually food isn't allowed to be stored within residents rooms.
•Before he turned cold he used to read bedtime stories in the living room for the younger residents. Jeff was his "favorite child" during the time he was fatherly to younger residents, but started to grow hatred and a reluctant tolerance for Jeff after he ended up having a horrible schizophrenic episode and killed a resident of the mansion who Slender once saw as valuable. (share more about that when I write my Jeff head canons)
•He renovated an old storage room in the mansion to be a make shift padded room, used as the ultimate punishment for residents that have become a danger to themselves or others. There isn't a lot of rules in the mansion but killing residents, harming residents and harming the mansion (remember this mansion is sentient) are taken very seriously. However he is a hypocrite and will often go against his own rules in order to intimidate others, just to make sure everyone stays under his control.
•Major ego, major control freak.
•His brothers also have their own versions of the slender sickness however since he is so powerful, he actually has affected his own brothers minds to make them forget how to use their powers/sickness's. They don't even really know that they have these powers until later on in life where they accidentally trigger their powers when Slenderman doesn't have his influence on them.
•His name is actually William O'Brien, however his father resents humans and only ever say them as tools/food. The women than birthed the slender brothers was a human caught in a love sick delusion with the Operator, the Operator used her as a vessel to spawn his sons. The Operator planned to have her keep creating offspring until she gave birth to the perfect replica of the Operator. However, during the ritual (yes an actual ritual you nasties) she ended up getting pregnant with quadruplets and she stayed pregnant for 4 years before she went into labor. (More on the mother another time)
•Slenderman only went by Slenderman purely because that's what the local towns folk referred to him as when he started becoming a replacement for the old Operator and myths started to spread.
•Proxy's are vessels, lifelines, as long as he has a proxy, he cannot die from physical injuries. He will simply remanifest.
•Age doesn't affect s tree walker.
•The slenderman family species is called Tree Walker.
•Tree walkers can be borne from dying trees, or created through rituals.
•Back to less serious stuff, he is a huge tea fanatic.
•His bed is 2 normal twin sized beds welded together so their long enough.
•He wears a brown suit with a green under vest. and during the night he wears that stereotypical old man night wear WITH the silly cap as well.
•Doesn't like thunder storms. The booms make him irritable.
•Classic old man hates technology, he literally still writes with a type writer when making new documents.
•Has stereotypical OCD and absolutely hates mess.
•He is aro ace and has 0 attraction of any kind, the best you can hope for is to befriend him. In fact he thinks humans look odd, he doesn't like their faces specifically (No he isn't jealous, it is uncanny to him, yes this would insult his mother)
