It started as an informal online competition to create spooky paranormal pictures in Photoshop but ultimately spawned one of the most shocking stories in recent memory.
In 2009, Eric Knudsen who frequented the Something Awful internet forum and blog participated in the innocuous challenge and created a haunting image that would become known as the Slenderman.
Soon the image of the unusually tall, skinny man with pale white skin and a featureless face took on a viral life of its own. The character became an internet meme with countless pictures, videos and stories circulating online typically involving Slenderman stalking, abducting or traumatising victims, mainly children.
In 2014, when two then 12-year-old girls in a sleepy Wisconsin town stabbed their friend 19 times and left her for dead in the woods, they claimed they carried out the heinous act to appease the fictional character.
It's a nightmarish story that will be told in depth as a new HBO documentary called Beware The Slenderman airs this week in the US.
Emmy-winner and Academy Award nominee Irene Taylor Brodsky is behind the project which follows Anissa Weier and Morgan Geyser for 18 months, beginning with their arrests in May of 2014 for the attempted murder of their friend Payton Leutner.
Despite being stabbed 19 times, Payton remarkably survived the attack with the knife barely missing vital organs. She was found by a cyclist as she crawled out of the woods where her friends had left her to bleed to death.
A central task of the filmmakers was to examine the power and influence internet phenomenon such as the Slenderman meme can have on those who primarily conduct their lives online. It is a deep dive into the dark corners of the internet and how fragile minds can get lost in there.
Following the attack the girls told police that the mythical white-faced man had told them to do it. Police say the girls had plotted for months to carry out the attack to impress the Slenderman.