Before multi-user dungeon games, video game players could only play games on their own, unless another person was present on the other side of a game board (like Pong). But in 1978, students at Essex University in Britain changed that by creating the first MUD game.
MUDs are essentially games played in a virtual world in which players can move from scene to scene and chat with other players. They also generally have themes of science fiction or fantasy. After seeing a virtual worldlike game focused on dungeons and wizards called Zork, created by Massachusetts Institute of Technology students in the late 1970s, Roy Trubshaw, a student at Essex University, created MUD with the “dungeon” as an homage to the Zork creators.
Initially, the games were very simple, more of a way for people to communicate, but Richard Bartle, another student at Essex, connected it to the US-based ARPANET (also known as the precursor to the Internet), which connected players across continents. This design ended up being the precursor to massively multiplayer online role-playing games, such as the immensely popular World of Warcraft.