The most popular type of MMOG, and the sub-genre that did much to pioneer the category, is the massively multiplayer online role-playing game (MMORPG). MMORPG's descend from university mainframe computer MUD and adventure games such as Rogue on the PLATO System and Dungeon on the PDP-10 that pre-date the commercial games industry.
The first graphical MMOG, and a major milestone in the creation of the genre, was the multi-player flight combat simulation game Air Warrior by Kesmai on the GEnie online service, which first appeared in 1987.
Commercial MMORPGs gained early acceptance in the late 1980s and early 1990s. The genre was pioneered by the GemStone series on GEnie, also created by Kesmai, and Neverwinter Nights, the first such game to include graphics, which debuted on AOL in 1991.
As computer game developers applied MMO ideas to other computer and video game genres, new acronyms started to develop, such as MMORTS. MMOG emerged as a generic term to cover this growing class of games. These games became so popular that a magazine, called Massive Online Gaming, released an issue in October 2002 hoping to cover MMOG topics exclusively, but it never released its second issue.
The debuts of Ultima Online and EverQuest in the late 1990's popularized the MMORPG genre. The growth in technology meant that where Neverwinter Nights in 1991 had been limited to 50 simultaneous players (a number that grew to 500 by 1995), by the year 2000 a multitude of MMORPG's were each serving thousands of simultaneous players.
Despite the genre's focus on multiplayer gaming, AI-controlled characters are still common. NPCs and mobs who give out quests or serve as opponents are typical mostly in MMORPGs. AI-controlled characters are not as common in action-based MMOGs.
The popularity of MMOGs was mostly restricted to the computer game market until the sixth-generation consoles, with the launch of Phantasy Star Online on Dreamcast and the emergence and growth of online service Xbox Live. There have been a number of console MMOGs, including EverQuest Online Adventures (PlayStation 2), and the multiplatform Final Fantasy XI (PC, PS2 {except in Europe} and now Xbox 360).
On PCs, the MMOG market has always been dominated by successful fantasy MMORPGs. In addition to Neverwinter Nights, Ultima Online and EverQuest, major entrants have included Asheron's Call, Ragnarok Online, Dark Age of Camelot, City of Heroes/Villans, Final Fantasy XI, and Lineage/Lineage2.
Science fiction has also been a popular theme, featuring games such as Anarchy Online, Eve Online, Star Wars Galaxies and The Matrix Online.
Several of the most recent successful MMORPG titles are Everquest 2, Lineage 2, Toontown Online (which is also the first aimed at families), World of Warcraft, Guild Wars, and Dungeons & Dragons Online: Stormreacha