if you look at the ED page it has a ton of info; SomethingAweful is the birth place of slender man though. Marble hornets is just a few friends who decided to make a video series based on fictitious events.
In short Marble Hornets started on YouTube. Slender Man started on SomethingAweful
I LOVE girls kissing girls! why you hatin'?
"After reading a few of your posts, I have decided that you are officially the CREEPIEST NS member." -AliGee
"i was so hungry i ate the Eucharist" -uncle.badness
take a shit in the shadow of the valley of death
"If this statement is not a homeless cardboard box man-orgy, then it is a shrimp." -Arabian.
R.I.P CR Johnson 2/24/10