A big starving male skeleton who lives with his brother, Papyrus, in the Underground. Him, his brother, and the other monsters were sealed away in a mountain. Eventually, they ran out of rations after the Core broke down. Leaving Horror Sans in an Underground suffering from famine. He convinced the entire Underground to eat humans, but he himself swore to never eat a human. His right eye socket is empty while his left eye socket holds a big red eye. He has a big gaping hole in his skull.