The Daedric prince of madness, in the Elder Scrolls series. In Skyrim he is the daedric prince in Pelagius Septim III's mind. If you play any of the Elder Scrolls games, you will know who he is.
Actually, no. I played Morrowind, Oblivion, and Skyrim. It's almost impossible to remember all the crazy names they come up with. I "knew" who he was, but I had to google the name to remember the connection.