Ever since JRR Tolkien published The Lord of the Rings in 1937, fantasy has had a far-reaching effect in many areas: literature, art, movies and gaming. Tolkien's novel provided a basis for many early gaming systems such as Advanced Dungeons and Dragons, but what it provided to tabletop gaming, it also provided to online, or computer gaming.
In 19761, Advent, the first of the text-based computer games, was created. Better known as Adventure, this was the prototype for interactive computer gaming, eventually spawning Multi-User Dungeons (MUDs). However, while running around killing the monster and getting the treasure was fun, more and more people began to role-play; establishing characters, creating their personalities, and building fictional lives around these bits of data. Code was developed which allowed people to create objects, giving them pillows that they could 'throw' at others - or allowing them to create Klingon Birds-of-Prey.
Eventually the original MUD code spawned variations which included:
MUCK - Basically MUD code that allowed you to open exits between players and objects instead of just rooms
MOO - MUD Object-Oriented
MUSH - Multi-User Shared Hallucination
The advent of MUCK and MUSH code allowed role-playing to go to a new level. Instead of the hack and slash mentality coupled with role-play that you would find on a MUD, a MUSH allowed folk to completely immerse themselves in a role-play world - expanding the characters that they created on a MUD into a complete persona. MUCKs and MUSHes based on author's worlds began to surface, such as Roger Zelazny's Amber novels and Anne McCaffrey's Dragonriders of Pern. People who wanted to be an Amberite or Impress (a telepathic dragon) could do so, with a little work and a lot of role-playing. More original worlds were created as well; places, for example, where people who wanted to role-play anthropomorphic animals in the style of comic books or animation (or Furries) were able to virtually become that being. Some of these places created their own combat systems - things more complicated than typing 'kill dragon'. Some eschewed any form of statistics to determine how a combat was played, preferring instead on consent and role-play to determine outcomes. Some used a combination of the two, giving stats, but strongly encouraging role-play as opposed to 'roll-play' ie, letting the dice or chance decide the outcome of a move.
Fantasy may have provided the basis for MUDs and MUD variations, but they expanded to encompass far more than just fantasy. Sci-fi lent a strong influence, prompting the creation of arcade games that led to the birth of Star Trek and many other science-fiction-based universes. The world of superheroes spawned places where one can have superpowers and fight evil, or plot to take over the world as a villain. World of Darkness M*s (MUDs and MUD variants) started with White Wolf's popular Vampire role-playing game (RPG) and expanded as the RPGs expanded. Social M*s, or talkers, were a haven for those who just wanted to hang out and chat. Places sprung up that were an amalgamation of many different genres, allowing people one place to scratch whatever itch they felt like instead of having to jump from place to place. A whole lexicon of terms came to be used, creating a new language to define the worlds in which these people played.
After more than 20 years in existence, and despite the proliferation of computer games and pay-to-play RPGs such as Everquest, the text-based M* is still going strong. There are both subscription-based and free games available in all genres. A couple of excellent sources to find places to play are The Mud Connector and MUSH Warehouse, both of which provide access to role-playing-based M*s, with descriptions and links so you can go directly to the site to see what the game is like.
A good rule of thumb to follow if you've never role-played before is to read all the help files, and to learn as much as you can before you even create a character. Some places will let you create whatever you like, and some limit you as to what roles they will allow you to play. Work out your character concept ahead of time - get a feel for the being you're going to create. If you're going to be playing in an M* based on an author's work, it never hurts to at least have a little familiarity with the world. Read the books - who knows, you might enjoy them. Don't be afraid to ask for help; staffers are there to assist you when you have questions. Correct spelling and grammar, while not generally required, do help to make a favourable impression. You will find that many people will be more receptive to well-done role-play, and consider those two things to be a part of good role-playing. If you're not a perfect speller, it's okay - spell-checkers are your friends. Above all, have fun with it. That is essentially what role-playing should be - something you enjoy.