Before there were the current generations of MMOs there were MUDs – multi-user dungeons or ‘dimensions’. And before there were MUDs there was MUD: A multi-player, text-based game running off a mainframe at Essex University.

MUD (known as MUD1 since the release of its successor, MUD2) used an interface similar to that of single player text adventure games and transplanted it to a multi-player realm where players could live virtual lives, solving puzzles, collecting treasure and killing fantastic creatures (and/or each other). The game launched in 1978, developed by Essex students Roy Trubshaw and, later, Richard Bartle.

via The birth of MMOs: World of Warcraft’s debt to MUD – games – Software – Techworld.