"Tom Clancy's Rainbow Six is a media franchise created by American author Tom Clancy about a fictional international counter-terrorist unit called "Rainbow." The franchise began with Clancy's novel Rainbow Six, which was adapted into a successful series of tactical first-person shooter video games, and is a planned future film tentatively set for release in 2010.
The first game was developed by Red Storm Entertainment, while the novel was being written. The game later spawned a number of sequels and expansion packs. Red Storm was later acquired by Ubisoft, who currently develops and publishes the games. Mobile phone versions of the game are developed and published by Gameloft.
Rainbow Six and its sequels defined the tactical shooter genre, forcing players to focus more time and effort on stealth, teamwork, and tactics rather than on sheer firepower. With some of the more recent releases; however, the game has taken on more of a "mainstream" first-person shooter approach in an attempt to appeal to a wider audience by moving away from the tactical planning aspect that made the game popular in the first place. This is due to several factors, the most prominent being the buy out of Clancy-owned Red Storm Entertainment by Ubisoft Entertainment."
Source: Wikipedia, "Tom_Clancy's_Rainbow_Six", available under the CC-BY-SA License.