A schizophrenic and insane skeleton who was forced to kill all (or, in some timelines, half) the monsters in the underground, including his own brother. He is hellbent on killing the human no matter what it takes. Despite this, he still believes they once wanted to do the right thing. A ghost of his brother, Papyrus, also follows him around and talks to him, but this is just a hallucination, and no one else can see or hear this "Phantom Papyrus".