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A Dungeon Master (DM), or Game Master (GM), is the planner, narrator, and referee of a tabletop role-playing game. Matthew Mercer is the DM of the canonical Critical Role episodes and some of the special episodes. Liam O'Brien was the DM for "Critical Role EXTRA – Liam's Quest!" (Sx12), "Critical Role Extra – The Return of Liam!" (Sx15), and "Liam's Quest: Full Circle" (Sx16).