game master

noun2

1. •
   A person (especially a man) conducting a game.

   • Using only meaning-laden glances or other undetectable gestures, the Mafia members indicate to the game master which villager they’d like to off. — 2007
2. •
   A person (especially a man) conducting a role-playing game, generally responsible for controlling all beings and processes other than the players, either individually or as part of a team.