doppelganger

noun
  1. 1

    A ghostly double of a living person, especially one that haunts such a person.

  2. 2

    An evil twin.

  3. 3

    A remarkably similar double; a lookalike.

  4. 4

    A monster that takes the forms of people, usually after killing them.

Source: https://en.wiktionary.org/wiki/doppelganger