It’s Nine Circles. I don’t need to describe it to you as it is one of if not the most iconic demons in the game’s history. While I have a form of epilepsy that prevents me from fully enjoying it, the fact that it changed the game on such a colossal scale, and the fact that it had an entire update make the majority of the community want to emulate it should speak for something. 6/10 for the epilepsy.