In computer gaming, a MUD (Multi-User Dungeon), pronounced /mʌd/, is a multi-user real-time virtual world described entirely in text. It combines elements of role-playing games, hack and slash, interactive fiction, and online chat. Players can read descriptions of rooms, objects, other players, non-player characters, and actions performed in the virtual world. Players interact with each other and the world by typing commands that resemble a natural language.
Traditional MUDs implement a fantasy world populated by fictional races and monsters, with players being able to choose from a number of classes in order to gain specific skills or powers. The object of this sort of game is to slay monsters, explore the world, complete quests, go on adventures, create a story by roleplaying, and otherwise 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 virtual assets, while others charge a monthly subscription fee. 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, like The Mud Connector.
It has been argued that modern games like World of Warcraft, and social virtual worlds such as Second Life can have their origins traced back to the early MUDs. Originally graphical virtual worlds were called graphical MUDs, most notably Everquest, but by 2000 the term MMORPG (massively multiplayer online role-playing game) had become the standard. The MMORPG RuneScape started out as a text-based MUD before graphics were added. Many MUDs are still active and a number of influential MMORPG designers, such as Raph Koster, Brad McQuaid, Mark Jacobs, Brian Green, and J. Todd Coleman, began as MUD developers and/or players.
Colossal Cave Adventure, created in 1975 by Will Crowther on a DEC PDP-10 computer, was the first widely used adventure game. The game was significantly expanded in 1976 by Don Woods. Adventure contained many D&D features and references, including a computer controlled dungeon master.
Inspired by Adventure, a group of students at MIT, wrote a game called Zork in the summer of 1977 for the PDP-10 minicomputer which became quite popular on the ARPANET. Zork was ported under the name Dungeon to Fortran by a programmer working at DEC in early 1978.
In 1978 Roy Trubshaw, a student at Essex University in the UK, started working on a multi-user adventure game in the MACRO-10 assembly language for a DEC PDP-10. He named the game MUD (Multi-User Dungeon), in tribute to the Dungeon port of Zork, which Trubshaw had greatly enjoyed playing. Trubshaw converted MUD to BCPL (the predecessor of C), before handing over development to Richard Bartle, a fellow student at Essex University, in 1980. 
MUD, better known as Essex MUD and MUD1 in later years, ran on the Essex University network until late 1987. The game revolved around gaining points till one achieved the wizard rank, giving the player immortality and certain powers over mortals. The game became more widely accessible when a guest account was set up that allowed users on JANET (a British academic computer network) to connect between the hours of 2 am and 8 am and at weekends. MUD1 was reportedly closed down when Richard Bartle licenced MUD1 to CompuServe, and was getting pressure from them to close Essex MUD. This left MIST, a derivative of MUD1 with similar gameplay, as the only remaining MUD running on the Essex University network, becoming one of the first of its kind to attain broad popularity. MIST ran until the machine that hosted it, a PDP-10, was superseded in early 1991.
During the Christmas of 1985, Neil Newell, an avid MUD1 player, started programming his own MUD called SHADES because MUD1 was closed down during the holidays. Starting out as a hobby, SHADES became accessible in the UK as a commercial MUD 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.
In 1985 Pip Cordrey gathered some people on a BBS he ran to create a MUD1 clone that would run on a home computer. The tolkienesque MUD went live in 1986 and was named MirrorWorld.
1985 also saw the creation of Gods by Ben Laurie, a MUD1 clone that included online creation in its endgame. Gods became a commercial MUD in 1988.
In 1985 CompuNet started a project named Multi-User Galaxy Game as a Science Fiction alternative to MUD1 which ran on their system at the time. When one of the two programmers left CompuNet, the remaining programmer, Alan Lenton, decided to rewrite the game from scratch and named it Federation II (there never was a Federation I). The MUD was officially launched in 1989.
In 1978, around the same time Roy Trubshaw wrote MUD, Alan E. Klietz wrote a game called Milieu using Multi-Pascal on a CDC Cyber 6600 series mainframe which was operated by the Minnesota Educational Computing Consortium. Klietz ported Milieu to an IBM XT in 1983, naming the new port Scepter 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 was first owned and run by GamBit (of Minneapolis, Minnesota), founded by Bob Alberti. GamBit's assets were later sold to InterPlay (of Fairfax, Virginia). InterPlay eventually went bankrupt.
In 1984, Mark Peterson wrote The Realm of Angmar, beginning as a clone of Scepter of Goth. In 1994, 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.
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 closed on February 10, 2007.
In the summer of 1980 University of Virginia classmates John Taylor and Kelton Flinn wrote Dungeons of Kesmai, a six player game inspired by Dungeons & Dragons which used Roguelike ASCII graphics. They founded the Kesmai company in 1982 and in 1985 an enhanced version of Dungeons of Kesmai, Island of Kesmai, was launched on CompuServe. Later, its 2-D graphical descendant Legends of Kesmai was launched on AOL in 1996. The games were retired commercially in 2000.  
The popularity of MUDs of the Essex University tradition escalated in the USA during the late 1980s when affordable personal computers with 300 to 2400 bit/s modems enabled role-players to log into multi-line Bulletin Board Systems and online service providers such as CompuServe. During this time it was sometimes said that MUD stands for "Multi Undergraduate Destroyer" due to their popularity among college students and the amount of time devoted to them.
The first popular MUD codebase was AberMUD, written in 1987 by Alan Cox, named after the University of Wales, Aberystwyth. Alan Cox had played the original University of Essex MUD, and the gameplay was heavily influenced by it. AberMUD was initially written in B for a Honeywell L66 mainframe under GCOS3/TSS and later ported to C in late 1988, which enabled it to rapidly spread to many Unix platforms when it was released in 1989. AberMUD's popularity resulted in several inspired works, the most notable of these were TinyMUD, LPMud, and DikuMUD.
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. 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. Monster, having about 60.000 lines of code, had a lot of features which appeared to be designed to allow Colossal Cave Adventure to work in it. In order to play Monster each player had to run a copy of Monster which communicated with other copies through shared files. This setup prevented Monster from gaining broad popularity, but it did inspire James Aspnes to create a stripped down version of Monster using the typical client-server model, which he named TinyMUD.
TinyMUD, written in C and released in late 1989, spawned a number of descendants, including TinyMUCK and TinyMUSH. TinyMUCK versions 2 contained a full programming language named MUF (Multi-User Forth), while TinyMUSH greatly expanded the command interface. To distance itself from the combat-oriented traditional MUDs it was said that the "D" in TinyMUD stood for Multi-User "Domain" or "Dimension", which led to the eventual adoption of the term MU* to refer to TinyMUD and its derivatives. UberMUD, UnterMUD, and MOO were inspired by TinyMUD but are not direct descendants.
In 1989 LPMud was developed by Lars Pensjö (hence the LP in LPMud). Pensjö had been an avid player of TinyMUD and AberMUD and wanted to create a world with the flexibility of TinyMUD and the power of AberMUD. In order to accomplish this he wrote what is nowadays known as a virtual machine which he called the LPMud driver as well as the C-like LPC programming language used to create the game world. Pensjö's interest in LPMud eventually waned and development was carried on by others. During the early 1990s, LPMud was one of the most popular MUD codebases.
In 1991, the release of DikuMUD, which was inspired by AberMUD, led to a virtual explosion of hack and slash MUDs based upon its code. DikuMUD inspired several derivative codebases too, most notably CircleMUD, Merc, and SillyMUD.
In 1987 David Whatley, who in previous years had played Sceptre of Goth and Island of Kesmai, founded Simutronics with Tom and Susan Zelinski. In the same year they demonstrate a prototype of GemStone to GEnie. After a short-lived instance of GemStone II, GemStone III was officially launched in February 1990. GemStone III became available on AOL in September 1995, followed by the release of DragonRealms in February 1996. By the end of 1997 GemStone III and DragonRealms had become the first and second most played games on AOL.
While there have been many variations in game-play and features in MUDs, some distinct sub-groups have formed that can be used to help categorize different the varieties.
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.
Hack and Slash MUDs
Due to the room based nature of traditional MUDs ranged combat is difficult to implement, as a result most MUDs equip characters with close-ranged weapons and usually takes place in a medieval fantasy setting. MUDs that restrict player killing and primarily focus on combat and questing are labeled Hack and Slash MUDs.
Player versus Player MUDs
Most MUDs restrict player versus player combat, often abbreviated as PK (Player Killing). This is accomplished through hard coded restrictions and various forms of social intervention. MUDs without these restrictions are known as PK MUDs and generally attract young males.
Roleplaying MUDs, generally abbreviated as RP MUDs, encourage or enforce that players act out the role of their playing characters at all times. Some RP MUDs provide an immersive gaming environment, while others only provide a virtual world with no game elements. MUDs that are heavily roleplay-enforced and have a cohesive game world are also known as RPI (Roleplay Intensive) MUDs.
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. Talkers create very little network traffic, making them ideal for setting up quietly at work. People who are long time users of ew-too talkers are called spods.
Psychology and playing style
Observations of MUD-play show styles of play that can be roughly categorized. Achievers focus on the difficulties of the game, difficult quests, fearsome monsters, and hard to obtain equipment; others explore every nook and cranny of the game, and try out all the guilds and races; some devote most of their energy to interacting with other players; then there are the killers who focus on interacting negatively with other players, if permitted, killing their characters or otherwise thwarting their play. Few players play only one way, or play one one way all the time; most exhibit a diverse style. According to Richard Bartle, a longtime coder and observer of MUD-play, responding to a question posed by Keith Stuart, an interviewer for The Guardian, "People go there as part of a hero's journey - a means of self-discovery"
- Keith Stuart (2007). "MUD, PLATO and the dawn of MMORPGs". "The thing is, though, that even if the likes of Oubliette did count as a virtual world, they had pretty well zero effect on the development of today's virtual worlds. Follow the audit trail back from World of Warcraft, and you wind up at MUD."
- Richard Aihoshi (2000-09-27). "Brad McQuaid Interview". RPG Vault. "Then, in 1996, I was hired by Sony Interactive Studios to create a graphical, commercial MUD. The rest is history."
- Jason Dobson (2007). "Q&A: Behind RuneScape's 1 Million Subscriber Success". Gamesutra. Retrieved on 2008-12-05. "When I went to university, I discovered text-based MUDs, or multi-user dungeons. I loved the fact that these sorts of games had all these players playing at once - even when you were not playing, the world carried on without you. Because of this, I began creating my own text-based MUD, but I quickly realized that with so many of them out there, there was no way that mine would ever get noticed. So I began to search for a way to make mine stand out, and the obvious way, of course, was to add graphics. With my game, I was trying to emulate text MUDs at the time, purely as a hobby."
- John Funk (2008). "WarCry and Jagex Talk RuneScape". WarCry Network. Retrieved on 2009-01-06. "Olifiers began with a brief history of Jagex and RuneScape: how Lead Developer Andrew Gower and his brother Paul founded the company in Cambridge in 2001, bringing their love for classic MUDs into the visual realm. The original RuneScape (now referred to as RuneScape Classic) was simply and exactly that: a 2D graphical interface placed on top of a MUD"
- Mike Nelson. "Interview: Brad McQuaid". The guru of 3D. Retrieved on 2007-03-03.
- Nick Montfort (2003). Twisty Little Passages: An Approach to Interactive Fiction. MIT Press. ISBN 354063293X. http://books.google.com/books?id=XiJFORKEm0oC.
- Bill Stewart. "Summary MUD History". "Containing many of the features of a D&D game, it added an interesting twist -- the dungeon master, the person who set-up and ran a D&D world, was played by the Adventure computer program itself."
- Tim Anderson. "The History of Zork". "Zork was too much of a nonsense word, not descriptive of the game, etc., etc., etc. Silly as it sounds, we eventually started calling it Dungeon. (Dave admits to suggesting the new name, but that's only a minor sin.) When Bob the lunatic released his FORTRAN version to the DEC users' group, that was the name he used."
- Kevin Kelly, Howard Rheingold (1993). "The Dragon Ate My Homework". Wired 1 (3). http://www.wired.com/wired/archive/1.03/muds.html. "In 1980, Roy Traubshaw, a British fan of the fantasy role-playing board game Dungeons and Dragons, wrote an electronic version of that game during his final undergraduate year at Essex College. The following year, his classmate Richard Bartle took over the game, expanding the number of potential players and their options for action. He called the game MUD (for Multi-User Dungeons), and put it onto the Internet.".
- Richard Bartle (2003). Designing Virtual Worlds. New Riders. pp. 741. ISBN 0131018167. "The "D" in MUD stands for "Dungeon" [...] because the version of ZORK Roy played was a Fortran port called DUNGEN."
- "Early MUD History" (1990). "The program was also becoming unmanageable, as it was written in assembler. Hence, he rewrote everything in BCPL, starting late 1979 and working up to about Easter 1980. The finished product was the heart of the system which many people came to believe was the "original" MUD. In fact, it was version 3."
- Richard Bartle. "Incarnations of MUD". "This is the "classic" MUD, played by many people both internal and external to the University. Although eventually available only during night-time due to the effects of its popularity on the system, its impact on on-line gaming has been immense. I eventually closed it down on 30/9/87 upon leaving Essex University to work for MUSE full time."
- Bill Wistner (1990). "A brief history of MUDs". "The point of the game was to gain points until you achieved the rank of wizard, at which point you became immortal and gained certain powers over mortals. Points were scored by killing things or dropping treasure into a swamp. The game gained some popularity in Britain when a guest account was set up that allowed users on JANET (the British academic network) to play during the small hours of the morning each day."
- Michael Lawrie (2003). "Escape from the Dungeon". "October of 1987 was chaos. The MUD account was deleted, but the guest account on Essex University remained open. I guess it wasn't causing any trouble so they simply left it. ROCK, UNI and MUD all ran from the MUD account so they had gone but... MIST ran from a student account and it was still playable."
- Kate & Frobozz (1986). "Micronet's Multi-user Game". Commodore Computing International. http://games.world.co.uk/shades/inshades/history/Mags.htm. "Written by Neil Newell, originally as a hobby because he enjoyed playing- the original MUD so much on Essex University, SHADES has recently. been launched on Micronet, the computer network, which has a large Commodore user-base.".
- Indra Sinha (1999). The Cybergypsies: a True Tale of Lust, War, and Betrayal on the Electronic Frontier.. Viking Press. ISBN 0-67088-630-0.
- Richard Bartle (1990). "Interactive Multi-User Computer Games". "Pip Cordrey used to run a BBS called 'Labbs', which had a section devoted to MUD1 in its early days. Six people from St. Paul's School worked on that section, and Cordrey organised them into a team to develop a MUA that would run on a home computer. The system was named MirrorWorld because it had rolling resets (as in the film "Westworld"). It went live in 1986."
- Richard Bartle (1990). "Interactive Multi-User Computer Games". "Although the present system went live in October 1988, Gods began in 1985 as a non-commercial MUA; its author was inspired by MUD1 to write his own game, and was among the first people to do so. Gods was Shades' only rival to be the Prestel Micronet MUA."
- Richard Bartle (1990). "Interactive Multi-User Computer Games". "The Multi-User Galaxy Game project was begun in 1985 by CompuNet as a SF alternative to MUD1, which then ran on the system. When the other programmer left CompuNet, Lenton rewrote the game from scratch as Federation II. It was officially launched on CompuNet in 1989; reported also to run on MicroLink, and on any other commercial system willing to take it."
- Bill Wisner (1990). "A brief (and very incomplete) history of MUDs". "Milieu was originally written for a CDC Cyber owned by the Minnesota Educational Computer Consortium. High school students from around the state were given access to the machine for educational purposes; they often ended up writing chat programs and games instead. I am uncertain of the precise time frame, but I believe Milieu probably predates MUD."
- Alan Klietz (1992). "Scepter - the first MUD?". "As micros became cost effective, the MECC mainframe became obsolete and was shut down in 1983. Scepter then went commercial in a collaboration between several ex-MECC (and by then also post-highschool) game hackers. It was rewritten in C and ran on a PC XT running QNX. It supported 16 dialup users, and dialup installations were set up in 5 states and Canada. This exposed Scepter to a lot of budding MUD developers at a time when the Internet was just getting started."
- Darrin Hyrup. "The Future of Dragon's Gate". "So after more than 15 years of great memories, with a heavy heart, I am going to officially declare Dragon's Gate closed... at least for now."
- Adrian Kennelly (2006). "Massive Multiplayer Online Role-Playing Games". "The first mainstream product was sold to the public in 1984. The game, Islands of Kesmai, was extremely expensive, and the graphics were anything but impressive."
- Raph Koster (2000). "Online World Timeline". ""My memory says that Island of Kesmai went live on CompuServe on December 15, 1985, after a very long internal test. The price was actually $6 an hour for 300 baud, $12 for 1200 baud. Serious players paid the bucks." - Kelton Flinn In (2000) May, Electronics Arts announces the shutdown of most of the Kesmai games, including Legends of Kesmai and Air Warrior Classic."
- Mark Gallear (1998). "An Economic History of the Game Industry". "The company continued to develop massively multiplayer games such as Air Warrior 2 (1997) and Legends of Kesmai (1996), distributing their games through AOL and eventually their own gaming service, GameStorm."
- "A Study of MUDs as a Society" (1998). "Some would insist however that 'MUD' does in fact stand for Multi Undergraduate Destroyer, in recognition of the number of students who may have failed their classes due to too much time spent MUDding!"
- Eddy Carroll. "5. Reviews -- Restf of the World". "Cox was a player of MUD1 who wrote AberMUD while a student at the University of Wales, Aberystwyth."
- Richard Bartle (2003). Designing Virtual Worlds. New Riders. pp. 741. ISBN 0131018167. "AberMUD spread across university computer science departments like a virus. Identical copies (or incarnations) appeared on thousands of Unix machines. It went through four versions in rapid succession, spawning several imitators. The three most important of these were TinyMUD, LPMUD, and DikuMUD."
- Richard Skrenta (1988). "monster - multiuser adventure game for VMS". "Monster was written in VMS Pascal under VMS 4.6."
- Richard Skrenta (1988). "An Introduction to Monster". "Monster allows players to do something that very few, if any, other games allow: the players themselves create the fantasy world as part of the game. Players can create objects, make locations, and set up puzzles for other players to solve."
- Richard Skrenta (1988). "An Introduction to Monster". "Each player who plays the Monster game runs a separate copy of the game. Each individual Monster process shares a database containing all of the information about the simulated world,"
- James Aspnes (1990). "Monster". "TinyMUD 1.0 was initially designed as a portable, stripped-down version of Monster (this was back in the days when TinyMUD was designed to be up and running in a week of coding and last for a month before everybody got bored of it.)"
- Richard Bartle (2003). Designing Virtual Worlds. New Riders. pp. 741. ISBN 0131018167. "TinyMUD was deliberately intended to be distanced from the prevailing hack-and-slay AberMUD style, and the "D" in its name was said to stand for "Dimension" (or, occasionally, "Domain") rather than "Dungeon;" this is the ultimate cause of the MUD/MU* distinction that was to arise some years later."
- Lauren P. Burka (1995). "The MUDline". "August 19, 1989. Jim Aspnes announces the availability of TinyMUD to a few friends. Its port, 4201, is Aspnes' office number. TinyMUD is written in C for Unix, and was originally conceived as a front-end for IRC."
- George Reese (1995). "LPMud timeline". "Having fun playing Tinymud and Abermud, Lars Pensjö decides to write a server to combine the extensibility of Tinymud with the adventures of Abermud."
- William Stewart (2002). "MUD History". "The original LPMUD was written by Lars Pensjl and others, and became one of the most popular MUD's by the early 1990's."
- melanie Cambron (2002). "A chat with Elonka Dunin". "Simutronics was originally the brain-child of David Whatley. As a teenager, he'd been big into the old BBS days and had even written some Fantasy Game BBS software that he sold all over the world, and he did this all from his parents' home. He’d also gotten involved as a player in some of the early multiplayer games that were out there such as Sceptre and Island of Kesmai, and, like many others who play these games, he thought to himself, "I can do this too." So in 1987, at the age of 21, he founded Simutronics Corporation with Tom and Susan Zelinski."
- Elonka Dunin (2008). "Simutronics Timeline". "December, 1996 - GemStone III and DragonRealms are the top two titles (hours/month) in industry"
- "Hearts, Clubs, Diamonds, Spades: Players Who Suit MUDs" article by Richard Bartle in The Journal of Virtual Environments, Volume 1, Number 1 (July 1997)
- Keith Stuart (2007). "MUD, PLATO and the dawn of MMORPGs". "People go there as part of a hero's journey - a means of self-discovery"
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