Referee

The referee of a role-playing game is a player with a special job. Rather than playing a single character, he plays all the non-player characters in the game as well as presenting the current scenario or adventure to the players.

Games frequently have their own title for the referee and the job is variously referred to as the Game Master, Dungeon Master, Storyteller, storyguide, the Keeper, moderator, narrator, director, etc...