A Dungeon Master (DM) is the storyteller and game facilitator in the game of Dungeons and Dragons (D&D). They are responsible for creating and describing the game world, setting up challenges and encounters for the players, and controlling non-player characters (NPCs). The DM also interprets the rules of the game and resolves any disputes or issues that may arise during gameplay. They strive to create a fun and engaging experience for the players, while also challenging them.