地下城主（Dungeon Master的首字母缩写，简称“DM”）是进行龙与地下城系列桌上角色扮演游戏(TRPG)时组织玩家的游戏主持人，一般由精通游戏规则、经验丰富的老玩家担任。负责游戏剧情的设计，决定人物接下来遇到的冒险旅程。一般进行一次TRPG称为“跑团”。

要成为一个地下城主，比如在龙与地下城中，你至少需要“三宝书”即三本核心规则书：

还有一样也是必不可少的，那就是想像力。

In the Dungeons & Dragons (D&D) role-playing game, the Dungeon Master (often abbreviated as DM) is the game organizer and participant in charge of creating the details and challenges of a given adventure, while maintaining a realistic continuity of events. In effect, the Dungeon Master controls all aspects of the game, except for the actions of the player characters (PCs), and describes to the players what they see and hear.