GMs date to the early 1970s. They were used in play-by-mail games, where players chose actions to take such as moving armies and mailed their moves the GM. The GM would mail back updated versions of the game to all players after recording all the moves. Some early examples of other games with GMs include Ironclad, Blackmoor and Chivalry & Sorcery.
GMs may have any number of jobs, such as organizing and moderating role-playing games, developing nonplayer characters, and making sure game rules are followed. In tabletop role-playing games, they bring character's stories together, solve disputes, and controls aspects players aren't involved in. In online games, they often enforce rules and provide customer service.
Dungeons & Dragons was an animated television series based on the role-playing game. The show was produced by Marvel Productions and broadcast from 1983 to 1985 on Saturday mornings on CBS. The premise had six friends (Hank, Diana, Eric, Presto, Sheila and Bobby) take a ride in an amusement park and suddenly find themselves in a Heroic Fantasy setting simply called The Realm. They are instantly garbed in clothes fitting their character classes and quickly gain a companion in a unicorn foal named Uni. A Mysterious Benefactor, known only as Dungeon Master, gives each of them an enchanted item to help them survive in that world and promises to help them find a way home.