Jeff the Killer is one of the most famous killer characters in creepypasta. The story tells how, ruined by accident and violence, he carves his own facial skin into a permanent smile and murders sleeping victims while whispering "Go to sleep." A bleached-pale face and that slashed grin are the image that defines the character.
Alongside Slender Man, Jeff became an icon of internet horror and spawned countless fan works and variations. It is a textbook case of collective horror, where a single shocking image and a brief origin tale spread into a vast shared character.