Source : Webster's Revised Unabridged Dictionary (1913)

Mandator \Man*da"tor\, n. [L.]
   1. A director; one who gives a mandate or order. --Ayliffe.

   2. (Rom. Law) The person who employs another to perform a
      mandate. --Bouvier.

Source : WordNet®

mandator
     n : an authority who issues a mandate