The game was initially populated primarily by students at Essex, but as time wore on and we got more external lines to the DEC-10, outsiders joined in. Soon, the machine was swamped by games-players, but the University authorities were kind enough to allow people to log in from the outside solely to play MUD, so long as they did so between 2am and 6am in the morning (or 10pm to 10am weekends). Even at those hours, the game was always full to capacity.
– Richard Bartle, Early MUD history, 15 Nov 90.
The first MUD stood for Multi-User Dungeon, and games are still usually referred to by that name. The following sections describe how the first MUD’s were invented, and list some historical clients and servers: