Doppelgänger

"Doppelgänger" has come to refer (as in German) to any double or look-alike of a person—most commonly an "evil twin". The essential meaning of the German word is "doublewalker", someone who is walking the same way as another person does. The word is also used to describe the sensation of having glimpsed oneself in peripheral vision, in a position where there is no chance that it could have been a reflection. They are generally regarded as harbingers of bad luck. In some traditions, a doppelgänger seen by a person's friends or relatives portends illness or danger, while seeing one's own doppelgänger is an omen of death. In Norse mythology, a vardøgr is a ghostly double who precedes a living person and is seen performing their actions in advance.
(as posted in Wikipedia)