Nyarlathotep

Nyarlathotep is the god of nightmares and chaos in the Cthulhu Mythos, a fictional universe. It has many forms.
It is one of the oldest beings within the Mythos, along with Yog-Sothoth and Shub-Niggurath.
Unlike most other Mythos beings, Nyarlathotep enjoys interacting with humans (and other helpless critters) and then driving them mad. It is also credited with giving humans the atomic bomb, with hopes that humanity kills itself off.