A DOPPELGANGER IS a mysterious, exact double of a living person. It's a German word that literally translates to "double walker" or "double goer". A doppelganger isn't someone who just resembles you, but is an exact double, right down to the way you walk, act, talk, and dress. A friend or even a close relative who encounters your doppelganger will swear it was you, even though you can prove you were not in the location the double was sighted.
Sightings and reports of doppelgangers have been around for centuries, and a great deal of superstition has developed around them. Traditionally, they have been viewed as sinister or even evil entities. Seeing a doppelganger has also been considered an omen of misfortune or bad luck.
Most often today, however - as reports of doppelgangers show - they seem to be neither sinister nor evil, nor do they herald streaks of bad luck. (Although some have been known to cause mischief.) They just seem to be, going about their business as if they are normal human beings. And perhaps they are.
Many reports of doppelgangers are probably cases of mistaken identity, but such an explanation becomes harder to accept when they are seen by best friends, siblings, and parents who know the real person intimately. It seems hard to believe that they would be fooled by another person who simply resembles the original. And how likely is it that they would have the exact same haircut and clothes, as is so often reported?
There have been several famous cases of doppelgangers, which you can read about in this article.
Another explanation for the phenomenon - and no less mysterious - is bilocation: a psychic projection of yourself - in every detail - that can appear in another place. This phantom self can even interact with other people.