DikuMUD is a multiplayer text-based role-playing game, which is a type of MUD. It was written in 1990 and 1991 by Sebastian Hammer, Tom Madsen, Katja Nyboe, Michael Seifert, and Hans Henrik Stærfeldt at DIKU (Datalogisk Institut Københavns Universitet)—the department of computer science at the University of Copenhagen in Copenhagen, Denmark.
Commonly referred to as simply “Diku”, the game was greatly inspired by AberMUD and LPMUD, though Diku became one of the first multi-user games to become popular as a freely-available program for its gameplay and similarity to Dungeons & Dragons. The gameplay style of the great preponderance of DikuMUDs is hack and slash, which is seen proudly as emblematic of what DikuMUD stands for.
Diku’s source code was first released in 1990.