A schizophrenic murderer that will do anything to stop the humans, even killing other monsters, even his own brother Papyrus, after so much killing he does secretly like it, but he's not all that, he actually hates and is disgusted at what he does, he is quite respectful to those he kills, even leaving money when he's stealing things even though he doesn't need to, due to his schizophrenia, he hallucinates seeing ghostly versions of his brother or his friends.