Doppelganger is a ghostly double of another character,
especially if it haunts its counterpart - a doppelganger, in german, means "double walker"
- it's like a carbon copy of a character with a different soul. However, one of the
criteria for a doppelganger isn't that it looks like its counterpart. Frankenstein and his
monster are considered to be doppelgangers.
from Leigh Averett
from Wikipedia
"Doppelgänger" has come to refer (as in German) to any double or look-alike of a
person—most commonly an "evil twin". The literal translation of the German word is
"double–goer", meaning someone who is acting (e.g. going) the same way as another person.
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 vardøger is a ghostly double who
precedes a living person and is seen performing their actions in advance.