Beware the Slenderman: Watch the Trailer for HBO's Bone-Chilling Documentary

First of all, let's go over who this "Slenderman" is. He was created in Photoshop for an Internet contest, and since he first debuted, writers and artists have included him in various works of fiction across the Internet. You can read a bunch of stories featuring the scary figure on the horror blog CreepyPasta. He's also the villain in several fan-made video games. You can read more about him right here.