Geometry Dash Doomsday was created by Neptune (IIINePtunEIII) and is an Insane level that has received a 9-star rating for its difficulty.
Neptune is a South Korean player and a creator of famous levels in the Geometry Dash community. He is the person who made a series of v2 levels famous, which are now even used as remakes. He is the one who created two famously difficult Demons, Necropolis and Deadly ClubStep. All of his levels are verified and have received positive ratings from RobTop. He is one of the six people who have achieved this. Some of the other people who have done this include Viprin, Michigun, AbstractDark, nSwish, and DeeperSpace.