I cannot remember when exactly I learned of Slenderman, but I do know that as long as I have known of him, I have believed him. I know others may not believe in him, and I know that some of them may think that people who do believe in him or claim to have seen him may be just imagining things, or tricking themselves into believing that he was really there. Yeah, I really do full-heartedly believe in Slenderman, but I can respect it if some people don't. I've heard of Der Ritter and Der Großemann and all that, but I've also heard a lot of people saying that those were fake, so I would not know what to say on that subject, but I've a theory or two as the Slenderman's origins. Yes, yes, forums or something; I do not know all about that part--frankly because I do not think that was the very beginning of Slenderman. Perhaps the first time he was publicly known, but definitely not how he was created, at least, in my views. I believe that he has existed since the beginning of ever, really, even if mankind was never aware of him. I think he is only known now because he wishes to be known where perhaps, a long time ago, he wished not to have anyone be aware of him at all. I think that on whichever forum he was "created" on, he was only there because he wished to be. About this special "Gift" I've seen mentioned a few times in a few places--I honestly do not believe that everyone has such a gift. I mean, certainly, many people do even if they choose not to acknowledge it, but I definitely believe the many people also do not have this gift at all, and that's the way it is, in my opinion. On the topic of "he's only real because you believe in him; if you didn't believe so strongly in him, he wouldn't be real," I do not agree with this. At all. I think either way, he exists. You can strongly believe he does. You can also strongly believe he does not. Either way--and not on this topic alone--simply because you believe something such as Slenderman exists (or does not exist) does not make it so.
So yeah. Those're my views and whatnot.