A game master, in Dungeons & Dragons and similar also dungeon master, is a person who is in charge of or who organizes a role-play, whether it be an online role-playing game or a role-playing video game. A game master may participate in the role-play they are in charge of, but this is often not the case. They are more likely to take up the role of fate or coincidence, and additionally also of a number of non-playable characters. A game master sometimes works together with one or more other game masters, who may take turns in deciding things, decide things together and/or each have their own specialty.

Game masters may or may not the Commanding Officer of their sim; this varies from club to club and sometimes within club.