The Collaborative International Dictionary of English v.0.48:

Stage director \Stage director\ (Theat.)
   One who prepares a play for production. He arranges the
   details of the stage settings, the business to be used, all
   stage effects, and instructs the actors, excepting usually
   the star, in the general interpretation of their parts.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

stage director
    n 1: someone who supervises the actors and directs the action in
         the production of a stage show