In computer gaming, a MUD (Multi-User Dungeon, Domain or Dimension) is a multi-player computer game that combines elements of role-playing games, hack and slash style computer games and social chat rooms. Typically running on an Internet server or bulletin board system, the game is usually text-driven, where players read descriptions of rooms, objects, events, other characters, and computer-controlled creatures or non-player characters (NPCs) in a virtual world. Players usually interact with each other and the surroundings by typing commands that resemble a natural language, usually English. Arguably, modern graphics-based massively multiplayer online role-playing games (MMORPGs), such as World of Warcraft, and social avatar virtual worlds such as Second Life can be considered MUD variants.

Traditional MUDs implement a fantasy world populated by elves, goblins, dwarves, halflings and other mythical or fantasy-based races, with players being able to take on any number of classes, including warriors, mages, priests, thieves, druids, etc., in order to gain specific skills or powers. The object of this sort of game is to slay monsters, explore a rich fantasy world, to complete quests, go on adventures, create a story by roleplaying, and/or advance the created character. Many MUDs were fashioned around the dice rolling rules of the Dungeons & Dragons series of games.

Such fantasy settings for MUDs are common, while many others are set in a science fiction–based universe or themed on popular books, movies, animations, history, and so on. Not all MUDs are games; some, more typically those referred to as MOOs, are used in distance education or for virtual conferences. MUDs have attracted the interest of academic scholars from many fields, including communications, sociology, law, and synthetic economies.

Most MUDs are run as hobbies and are free to players; some may accept donations or allow players to "purchase" in-game items, while others charge a monthly subscription fee.

The first games which might today be recognised as MUDs appeared in 1977 on the PLATO system.^{[citation needed]} In Europe at around the same time, MUD development was centered around academic networks, particularly at the University of Essex where they were played by many people, both within and outside of the university. In this context, it has been said that MUD stands for "Multi-Undergrad Destroyer" or "Multiple Undergraduate Destroyer" due to their popularity among college students and the amount of time devoted to the MUD by the student. The popularity of MUDs of the Essex University tradition escalated in the USA during the 1980s, when—relatively speaking—cheap, home personal computers with 300 to 2400 bit/s modems enabled role-players to log into multi-line BBSes and online services such as Compuserve.

The first known MUD was created in 1978 by Roy Trubshaw and Richard Bartle at Essex University on a DEC PDP-10 in the UK, using initially MACRO-10 (an assembly language) and, later, rewritten in BCPL; also used was a database description language, MUDDL.^[1] They chose the acronym MUD to stand for Multi-User Dungeon,^[2] in reference to a Fortran port of Infocom's text adventure game Zork for the PDP-10 called Dungeon (or DUNGEN due to the six character filename limit).^[3] Zork in turn was inspired by an older text-adventure game known as Colossal Cave Adventure or ADVENT. The classic game MIST (also part of Essex University MUD) which could be played from any computer connected to JANET (a European academic network), became one of the first of its kind to attain broad popularity.^[4]

Oubliette, written by Jim Schwaiger, and published on the PLATO system predated MUD1 by about a year. It was so difficult that one could not play it alone: in order for players to survive, they had to run in groups. While Oubliette was a multi-player game, there was no persistence to the game world. Following it, also on PLATO, was a game called Moria written in 1977, copyright 1978. Again, players could run in parties but in this game it was also possible to effectively play while only running one character. They were graphical in nature and very advanced for their time, but were proprietary programs that were unable to spread beyond PLATO. Textual worlds, which typically ran on Unix, VMS, or DOS, were now far more accessible to the public.

Another early MUD was Avatar, begun around 1977 and opened in 1979, written by Bruce Maggs, Andrew Shapira, and Dave Sides, all high school students using the PLATO system at the University of Illinois. This MUD was 2.5-D game running on 512x512 plasma panels of the PLATO system, and groups of up to 15 players could enter the dungeon simultaneously and fight monsters as a team. Avatar, with by far the most hours played of any PLATO game, is still running, playable by anyone, on the emulated mainframe at www.cyber1.org and via the NovaNET NPT service.

In the late 1970s there were numerous other PLATO games which were MUD-like, in various stages of development, some open, some never opened. Some were essentially single-player games but had some multi-player interaction such as communication and shared halls of fame. These games influenced the development of more well-known PLATO MUDs such as Avatar and Oubliette. At the time, these games were referred to as 'dungeon games'. Around this time, at least 10 and possibly as many as 100 people were actively working on MUD games on PLATO. It was common to see two to five people sitting side by side and working on different MUD games in room 165 or the author room of University of Illinois's CERL building. Many non-MUD games also came from this environment, such as empire and airfight.

In 1978, Alan E. Klietz wrote a game called Milieu using Multi-Pascal on a CDC Cyber, which was used by high school students in Minnesota for educational purposes. Klietz ported Milieu to an IBM XT in 1983, naming the new port Scepter of Goth (also spelled Sceptre of Goth). Scepter supported 10 to 16 simultaneous users, typically connecting in by modem. It was one of the first commercial MUDs; franchises were sold to a number of locations. Scepter (and an unfinished advanced MUD by Klietz called ScreenPlay) was first owned and run by GamBit (of Minneapolis, Minnesota), founded by Bob Alberti. GamBit's assets, including Scepter and ScreenPlay, were later sold to InterPlay (of Fairfax, Virginia). InterPlay eventually went bankrupt, making Scepter no longer available. In 1984, Mark Peterson wrote The Realm of Angmar, beginning as a clone of Sceptre of Goth.

In 1984, Mark Jacobs created and deployed a commercial gaming site, Gamers World. The site featured two games coded and designed by Jacobs, a MUD called Aradath (which was later renamed, upgraded and ported to GEnie as Dragon's Gate) and a 4X science-fiction game called Galaxy, which was also ported to GEnie. At its peak, the site had about 100 monthly subscribers to both Aradath and Galaxy. GEnie was shut down in the late 1980s, although Dragon's Gate was later brought to America Online before it was finally released on its own. Dragon's Gate was officially closed on February 10th, 2007 until further notice.^[5]

These text-adventure games (both single and multi-player) drew inspiration from the paper-and-pencil based role-playing games (RPGs) that were approaching their peak popularity at this time, especially with the release of Advanced Dungeons & Dragons (AD&D) in 1977.

This strong bond between RPGs and MUDs continued through the years with the release of dozens of AD&D modules and related books and stories (e.g., Forgotten Realms and Dragonlance). Influences also came from the gamebooks such as Fighting Fantasy, Choose Your Own Adventure, and Lone Wolf.

Other MUDs that appeared around 1985 included Mirrorworld, run by Pip Cordrey and developed and written by Tim Rogers, Lorenzo Wood and Nathaniel Billington. Mirrorworld was the first MUD to feature rolling resets. SHADES by Neil Newell was a commercial MUD accessible in the UK via British Telecom's Prestel and Micronet networks. A scandal on SHADES led to the closure of Micronet, as described in Indra Sinha's net-memoir, The Cybergypsies.

Another popular MUD was AberMUD, written in 1987 by Alan Cox (also known as Anarchy), named after the University of Wales, Aberystwyth. Avalon, the Legend Lives, started in 1989, was the first MUD to combine a consistent fantasy story-line with a commercial venture. AberMUD was initially written in B for a Honeywell L66 mainframe under GCOS3/TSS and later ported to C, which enabled it to rapidly spread to many Unix platforms.^[6]

Monster was a multi-user adventure game created by Richard Skrenta for the VAX and written in VMS Pascal. It was publicly released in November 1988.^[7] Monster was disk-based and modifications to the game were immediate. Monster pioneered the approach of allowing players to build the game world, setting new puzzles or creating dungeons for other players to explore.^[8] Monster was the inspiration for TinyMUD.^[9]

In 1989, TinyMUD began to allow players to easily participate in creating the online environment, as well as playing in it. The TinyMUD code spawned a number of descendants, including TinyMUCK and TinyMUSH, which added more sophisticated programmability. (TinyMUCK versions 2 and higher contain a full programming language named MUF, or Multi-User Forth, while MUSH greatly expanded the variety of commands and functions available and allowed them to apply to all objects.) Some use the term MU* to refer to TinyMUD, MUCK, MUSH, MUSE, MUX, and their kin; others simply allow the term MUD to apply universally. MUVE is a recent coinage, intended to stand for Multi-User Virtual Environment. UberMUD, UnterMUD, and MOO are some other MUD servers that were at least partially inspired by TinyMUD but are not direct descendants.

Also in 1989, and inspired by TinyMUD and AberMUD, LPMud was developed as a more game-oriented MUD built around a C-like programming language, LPC. 1989 also saw the development of Avalon, using its own code base run through the Hourglass compiler. Developed in complete isolation from all other MUDs, Avalon adopted an object-oriented approach using the powerful British Acorn Archimedes computer technology. In Europe it was very popular for MUD writers to write in isolation. The three largest commercial examples would be Avalon, Shades and the Terris/Cosrin Engine.

In 1991, the release of DikuMUD, which was inspired by AberMUD, led to a virtual explosion of hack-n-slash MUDs based upon its code. DikuMUD inspired several derivative codebases too, including CircleMUD, Merc, ROM and SMAUG. Meanwhile, Avalon had become a commercial game operating in the UK on up to 16 simultaneous modem connections.

In 1992 a second Avalon, the Legend Lives site was opened in the north of England, Sheffield, to give local users cheaper phone call access.

In 1993 Avalon, the Legend Lives attempted to circumvent the expense of online connections in the UK with the Hostplay concept: providing access via terminals in Avalon's own offices in central London in addition to its 16 modem connections.

In 1994, Mark Peterson rewrote The Realm of Angmar, adapting it to MS-DOS (the basis for many dial-in BBS systems), and renamed it Swords of Chaos. For a few years this was a very popular form of MUD, hosted on a number of BBS systems, until widespread Internet access eliminated most BBSes.

Avalon, like other commercial MUDs, went live on the Internet in late 1994. In doing so, they closed down the local Sheffield site. It also released a specialized Windows telnet client named AvPlay, making it the first MUD to release such a client (although AvPlay can also be used for any other MUD.) Avalon, the Legend Lives is still running and under continuous development today.

The closing of the Sheffield site motivated one Avalon player, Paul Barnett (now creative Director for the Warhammer Online MMO at EA-Mythic), to design and write the Legends of Terris MUD engine with Doug Goldner. Paul Barnett designed the game and Doug Goldner wrote the code.

At this time, AOL US already ran several highly successful games, including Dragons Gate and Darkness Falls (by Mythic Entertainment, which later launched Dark Age of Camelot), Federation (game) (a space trading game) and Gem Stone III (Simutronics, which later launched A Hero's Journey), and AOL Europe had begun operations and was looking for a European MUD game to offer to its subscribers. Legends of Terris was selected to be AOL Europe’s flagship MUD. Legends of Terris was launched on AOL Europe at the end of the year. Legends of Terris itself was hosted at a place called Sub-Cyberia in the basement of the first UK Internet cafe, Cyberia. The game was also translated into German. Contemporary European commercial games typically had around 30-50 players connected at once; within one month, Legends of Terris had over 600 simultaneous players connected.

Legends of Terris became the largest commercial MUD in Europe^{[citation needed]}, with over 2000 simultaneous players connected at once. It was now generating over 250,000 game-hours worth of revenue for AOL. Legends of Terris would hit a number as high as 2,544 players at once, while Gem Stone III continued to dominate the commercial MUD world, attracting 6000 concurrent users at its height. Gem Stone III, Avalon and Legends of Terris are all commercially operating today.

Of the commercial engines available, Avalon focused on player vs. player design, Gem Stone III was dominant in the areas of game world size and installed player base, and Legends of Terris championed the player vs. environment style of play.

MUDs can be accessed via standard telnet clients, or specialized MUD clients which are designed to improve the user experience. Numerous games are listed at various web portals (see External Links).

Online graphics-based games (MMORPGs), such as EverQuest, World of Warcraft, Runescape, and Dungeons & Dragons Online: Stormreach, and graphics-based social avatar worlds like Second Life, are arguably analogous to MUDs, and are sometimes referred to as "graphical MUDs" (see next section) or "next-generation MUDs".

Similarities include the basic goals and objectives of the games, where games are present, and the sociality of the environments (the tendency to associate in or form social groups). One difference, among many, is that the majority of MMORPGs and social avatar worlds are commercial ventures. The Business of Social Avatar Virtual Worlds

A graphical MUD is a MUD that uses computer graphics to represent parts of the virtual world and its visitors. A prominent early graphical MUD was Habitat, written by Randy Farmer and Chip Morningstar for Lucasfilm in 1985. Graphical MUDs require players to download a special client and the game's artwork. They range from simply enhancing the user interface to simulating 3D worlds with visual spatial relationships and customized avatar appearances.

After the increase in computing power and Internet connectivity during the late nineties, graphical MUDs became better known as MMORPGs, Massively Multiplayer Online Role-Playing Games.

A less-known MUD variant is the talker, typically based on ew-too or NUTS, with plenty of derived codebases. The early talkers were essentially MUDs with most of the complex game machinery stripped away, leaving just the communication commands -- hence the name "talker". Talkers use simple protocols and create very little network traffic, making them ideal for setting up quietly at work.

People who use these tend to be called spods, and have earned a place in the Jargon File.

A player versus player, or player killing, MUD is one which encourages player versus player combat. Some MUDs have registered player killing, meaning a player must register as a player killer and can only fight other registered player killers.

A Roleplay intensive MUD is a MUD that is heavily roleplay-enforced. The RPIMUD Network describes a RPI MUD as a MUD that "center themselves around suspension of disbelief and playing out specific character roles as if the role were real and you were your character. In general, the objective of the game is not to complete computer-generated quests or tally the most kills in order to gain levels and equipment, but to collaborate with fellow players to create complex and multi-layered storylines in a cohesive gaming environment. RPIMUDs are very different from other MUDs because of the emphasis on character interaction over hack-and-slash gaming."

Dr. Sherry Turkle, Ph.D. of Sociology of Science at MIT, developed a theory in her book "Life on the Screen" that the constant use (and in many cases, overuse) of MUDs allows users to develop different personalities in their environments. She uses examples, which date back to the text-based MUDs of the mid-1990s, showing college students who simultaneously live different lives through characters in separate MUDs, up to three at a time, all while doing schoolwork. The students claimed that it was a way to "shut off" their own lives for a while and become part of another reality. Turkle claims that this could present a psychological problem of identity for today's youths.

Turkle also explores the ideas of the use of bots in MUDs. She references the Turing Test, put forth by Alan Turing, proposing that an automaton could be considered truly intelligent if they were able to convince a human conversing with it that it was human. Turkle presents the troubling ideas of sexual deviancy involved with this: that someone posing as a bot could "trick" someone into believing that they were a bot and allowing them to engage in sexual activity online. Turkle wonders aloud if this could be considered, at the worst, rape and at the very least, an invasion of privacy.

• Interactive fiction, a kind of single player "MUD"
• Category:MU* servers
• Category:MU* games
• MUD client
• MUD trees
• Mobile (MUD)
• MMORPG – Massive Multiplayer Online RPG
• MUSH
• MOO
• MUCK
• Talker - historically based on MUDs
• Online Creation
• Online text-based role-playing game
• Cyberformance

• Some history and reviews from Richard Bartle's "Interactive Multi-User Computer Games" report
• The MUDline: A timeline of MUD history up to 1995.
• A Classification of MUDs by Martin Keegan, Grandmaster Data Services Ltd, Cambridge, UK
• Early MUD history
• Online World Timeline - Raph Koster's timeline of significant events for the development of virtual worlds.
• Living Internet A comprehensive history of the internet, including MUDs.
• Bartle MUD Personality Analyzer Long-running test to classify MUD/MMORPG personality, based on Bartle's research.
• [2] Cultural Formations in Text-Based Virtual Realities.
• Journal of Virtual Environments: Formerly the Journal of Mud Research. A currently inactive peer-reviewed academic journal.

• Erwin S. Andreasen: Home of the 16k MUD competition, and other resources.
• ftpgame.org: Hierarchal archive of MUD source code
• MudBytes.net: MUD code repository and discussion.
• MudMagic.com: MUD software downloads, discussion, game listings, and documentations.
• Mindcloud.com: MUD code repository and discussion. Specifically dealing with the GodWars Derivative line.

• The MUD Connector: Large portal site containing 1300+ searchable listings of text-based MUDs, discussions, a social network devoted to mudding, resources, etc
• Jargon File: The Jargon File's entry on MUDs.
• Mapping MUDs: 3-Dimensional modelling of a MUD
• Mud Domain: The Social Network for Mudders
• MU*Wiki: A community site for discussion and promotion of MUDs.
• The MudLists Resource Center: A comprehensive list of over 600 MUDS including numerous player references and other MUD related statistics.
• Top Mud Sites: MUD portal and voting site containing 1700+ MUDS, MUD forums, reviews, resources, MUD articles.
• MUDseek: Google custom search engine indexing MUD and MUD-related web sites.
• RPIMUD Network: Site devoted to Role-Play Intensive MUDs.
• NoGFX (No Graphics): MUD logs and resource archive.
• FindMUD: MUD listings and codebase downloads.