Somebody's alternate personality or persona; another self.
A very close and intimate friend.
A corporation used by a person to conduct personal business in an attempt to shield himself or herself from personal liability, and which a court may penetrate by "piercing the corporate veil" to impose liability on the person when they commit fraud or injustice.
A ghostly double of a living person, especially one that haunts such a person.
An evil twin.
A monster that takes the forms of people, usually after killing them.
A remarkably similar double.