Source : Webster's Revised Unabridged Dictionary (1913)

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

         Either you are Hereward, or you are his doubleganger.
                                                  --C. Kingsley.