The Collaborative International Dictionary of English v.0.48:
Mandator \Man*da"tor\, n. [L.] 1. A director; one who gives a mandate or order. --Ayliffe. [1913 Webster] 2. (Rom. Law) The person who employs another to perform a mandate. --Bouvier. [1913 Webster]WordNet (r) 3.0 (2006):
mandator n 1: an authority who issues a mandate