Many fRPGs go so far as to make them a distinct species - or type of construct with a tendency to steal people's identities and murder them (which would explain why their appearance would be an omen of death).
The term can also be used to describe a ghostlike apparition of someone that appears to one or more people known to them as a herald of their death (as in the famous case of Admiral Tyron, who was seen to walk through the drawing room of his family home in London on the same night as he was drowned when his ship was lost in collision off the Syrian coast). This form of ghostly doppleganger is sometimes referred to as a fetch or death-fetch2.
Game and Story Use
- A doppelgänger can be a very frustrating foe for a player character simply by pretending to be them and committing nefarious deeds with which the PC will subsequently be accused of.
- As plot devices they can prove a useful excuse for an apparent face-heel (or indeed heel-face) turn by an NPC - or a change of player for a PC.
- It is possible that a doppelgänger results from the negative emotions in the psyche of a character - and it might be given physical form by magic (possibly by a botched spell).
- The Dopelgänger could turn out to be form of Tulpa.
- It could turn out to be a duplicate from an alternate reality.
- It could be a duplicate built specifically to replace the character for purposes of infiltration - or simply something from 'outside' that wants to steal their identity.
- A good origin story, particularly in an After the Fall setting, places them as infiltration/subversion units developed by Secret police or military intelligence and their attempts to interpret the orders of long dead masters can explain both bizarre behaviour and entirely logical replacement of pretty much any member of any instituitions.
- The Fair Folk are also an appropriate suspect in such cases.