The Slender Man (also known as Slenderman) is a fictional supernatural character that originated as an Internet meme created by Something Awful forums user Eric Knudsen (a.k.a. "Victor Surge") in 2009. It is depicted as resembling a thin, unnaturally tall man with a blank and usually featureless face, wearing a black suit.
During 2012, the game Slender began to become popular among YouTube. Many people asked Al if he could play it, and much to his displeasure with scary games, he did. While he only played 10 minutes of the game, it left him utterly terrified and promising himself he would not play another scary game again.
One year latter, the sequel, Slender: The Arrival, was released. This time Al had Matt from the RLF podcast play it for him, while he himself watched as a spectator. In the end, both of them shit their pants.
Ever since then the Slender Man has had an impact on Al, sometimes worrying that he will appear in mods.