Answer: Wizards of the Coast

Thanks to its widespread use in popular culture (well, at least, widespread within geek culture that is), it would be easy to assume that “dungeon master” was simply a generic term for whoever was in charge of coordinating a role-playing game. Traditionally, said person is responsible for selecting the module or adventure path, or even creating (homebrewing) the storyline the players will follow, taking on the roles of the non-player characters and monsters, mediating the game experience, and otherwise controlling all aspects of the game world except player actions.

While the game leading function might exist in multiple role-playing games, the only games where the leader of the experience is officially known as a “dungeon master” are Dungeons & Dragons and derivative games owned by Wizards of the Coast. In other game systems, alternative terms are used to describe the role including Game Master, Judge, Castle Keeper, Storyteller, or titles specifically related to the genre or style of the game like Keeper of Arcane Lore or such.