Noun: Doppleganger (DAH-pul-gang-er)
1. A ghostly counterpart of a living person.
2. A person who closely resembles another living person.
3. The opposite side of a personality: alter ego.
4. A person who has the same name as another.
Example sentence: Throughout the movie, the main character is frequently mistaken for someone else, and the plot thickens when this doppelganger turns out to be a wanted criminal.