A monster skeleton that has been through multiple resets in his timeline, dying and coming back over, and over again until he snaps and decided to dust/kill the entire Underground, including his brother, Papyrus. He usually resorts to alcohol, like vodka. 

He's careless, psychotic, and clearly schizophrenic, as he sees a ghost version of his brother, which he killed. Smart and reads a lot of books, violent yet calm at times. Wants to kill humans.