"Folklore, Horror Stories, and The Slenderman"
I very distinctly remember when Slenderman began trending online. My friends and I even played the Slenderman horror game, which was both fun and terrifying at the same time. The mystery surrounding the origins of Slenderman, as well as the fleshed-out character mythos made him very intriguing to our age group. Looking back, I can clearly see the perfect recipe that culminated in the popular spread of Slenderman. It is just like Victor Surge says, "an urban legend requires an audience ignorant of the origin of the legend".
As the article states, the platform that Slenderman was first conceived also plays a huge role in the popularization of the character. In recent years, the Reddit thread r/nosleep has transformed into the new Something Awful, churning out user-generated content that often makes its way to mainstream media. While every Reddit user is well aware that r/nosleep is purely fiction, the average Internet layman with little to no knowledge of Reddit will usually fall victim to the thread and take a few well-written stories to heart. A good example of a Slenderman-esque content creation is the story of Forest Stairs, where a reddit user crafted an extremely convincing account of discovering a set of stairs in the middle of the woods during his time as a forest ranger. Slowly, other users began building upon this story, resulting in the mythos spreading to other Reddit threads (funnily enough, the story made it to 'trending' on the National Park/Hikers thread, where it was received as a true account). Here is the link to the thread:
Just as how Slenderman was created in a relatively obscure, constrained platform, combined with his natural aura of mystery, stories like the Forest Stairs have become 'viral' due to similar reasons. Reddit users occupy a very specific portion of Internet users, and r/nosleep members make up an even smaller portion. Therefore, talented writers in r/nosleep often create a piece of fiction, and then sit back and watch as it transforms in the hands of other users until it makes it way to other threads and eventually, to mainstream media.