A GameMaster, in the purest sense, is the person who builds the scenarios, monsters, non-player characters, world, and mechanics that their players must grapple with. Now, for those who have the money or friends with money, there are shortcuts. Nearly every GameMaster uses an already-established gaming system (though they may mod it to their own tastes). Some GameMasters build their own world using popsicle sticks and bits of twine, and some use a well-known world like Faerun or the Rifts universe to set their campaign in.