FreeOrion

Master of Orion is a turn-based game. In the first iteration of the franchise, one can only play against the artificial intelligence (AI). Human and AI players control the management of colonies, technology development, ship construction, inter-species diplomacy, and combat.

The software generates a map randomly at the start of each game; the player can only choose the size of the galaxy, and the number and difficulty of AI opponents. In the first game, star systems have at most one colonizable planet and a few have none. Later games have more planets.

Master of Orion is a significantly expanded and refined version of the prototype/predecessor game Star Lords (not to be confused with Starlord, also released by MicroProse in 1993). Steve Barcia's game development company Simtex demonstrated Star Lords to MicroProse and gaming journalist Alan Emrich who, along with Tom Hughes, assisted Barcia in refining the design to produce Master of Orion; and the game's manual thanks them for their contributions. Emrich and Hughes later wrote the strategy guide for the finished product. MicroProse published the final version of the game in 1994.

Star Lords, often called Master of Orion 0 by fans, was a prototype and never commercially released (its intro opens with "SimTex Software and Your Company present"). The crude but fully playable prototype was made available as freeware in 2001, stripped of all documentation and copy protection, in anticipation of the launch of Master of Orion III. Major differences between Star Lords and Master of Orion include inferior graphics and interface, simpler trade and diplomacy, undirected research, a lack of safeguards to prevent players from building more factories than are usable and the use of transports rather than colony ships to colonize new planets. One feature of Star Lords that Master of Orion lacks is a table of relations between the computer-controlled races. The game was eventually made available for download on FilePlanet and the home page for Master of Orion III.

Master of Orion sold over 100,000 copies. It also received strong reviews. Emrich in a September 1993 Computer Gaming World preview described Master of Orion as "the best that galactic conquest can offer", and summarized its type of gameplay as "4X", meaning "eXplore, eXpand, eXploit, eXterminate". He and later commentators noted earlier examples of this genre, including Civilization (1991) and Reach for the Stars (1983).

The magazine's full December 1993 review stated that "Master of Orion is one of those games where one must actually put effort into finding something inadequate about the game design, and that in itself is probably the highest praise this reviewer can give a product". The magazine concluded that it was "a definite Game of the Year candidate as well as Exhibit A in many divorce cases". A February 1994 survey of space war games gave Master of Orion a grade of A−, stating that "it's still conquest, but it's conquest that begins to have an interesting point to it". The reviewer wished that the game supported multiple players, but predicted that "I think MOO will safely reign supreme well into the new year".

In 1996, Computer Gaming World ranked Master of Orion as the 33rd best game of all time. In 1998, PC Gamer declared it the 45th-best computer game ever released, and the editors called it "a great sci-fi space epic". In 2003, IGN ranked it as the 98th top game. Master of Orion is a member of both GameSpy's Hall of Fame (2001) and GameSpot's list of the greatest games of all time. The Gamer included it in their list of top 10 games in the 4X genre.

In retrospective reviews, Allgame, GameSpot and IGN regarded MoO as the standard by which turn based strategy games set in space are judged.