doppelganger
One of:
* a remarkably similar double; a lookalike,
* an apparition or ghostly double of a living person; especially one that haunts such a person,
* the opposite side of a personality; an alter ego; an evil twin,
* a person who has the same name as another; an imposter, or
* a monster that takes the forms of people, usually after killing them.
Aliases: none