doubleganger

from The Collaborative International Dictionary of English v.0.48

Doubleganger \Dou"ble*gang`er\, n. [G. doppelg[aum]nger; doppel
   double + g[aum]nger walker.]
   An apparition or double of a living person; a
   doppelg[aum]nger.

         Either you are Hereward, or you are his doubleganger.
                                                  --C. Kingsley.
   [Webster 1913 Suppl.]