Source : Webster's Revised Unabridged Dictionary (1913)

Appropriator \Ap*pro"pri*a`tor\, n.
   1. One who appropriates.

   2. (Law) A spiritual corporation possessed of an appropriated
      benefice; also, an impropriator.

Source : WordNet®

appropriator
     n : someone who takes for his or her own use (especially without
         permission)