Doppelganger

A doppelgänger is a supernatural double of a living person, especially one who haunts the doubled person. In fiction and mythology and in common parlance, the doppelgänger either is a ghost or a paranormal phenomenon, usually perceived as the harbinger of bad luck. A literary example of a doppelgänger is the evil twin of the protagonist. In modern times, the term twin stranger is occasionally used.