doppelganger

noun

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

   “"An orderly let out the news that you are here," she said. "But don't worry. We've sent out a doppelganger to fool the Sons, and the orderly has been sentenced to slavery under the pyramid builder for twenty lifetimes. I hate my brother! How dare he fight us with the sky falling?"”

   “The uncanniness provoked by doppelgangers is particularly acute because the thing that becomes unfamiliar is you.”

2. An evil twin.
3. A remarkably similar double.

   “Stars in Their Eyes ran for 16 years from 1990, and had the "wow" factor moment of transforming a pub singer into their idol, as the contestant said the famous words: "Tonight Matthew, I'm going to be…" and then stepped out from a puff of dry ice as their musical doppelganger.”

   “He had come tantalisingly close to his doppelganger on Thursday night when a beautiful burgundy boat cruised past him. “He saw me and I waved and he gave me a thumbs-up,” said Halicilar. “I was so happy. I cried.””

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