Rainbow was formed by ex-CIA operative John Clark (dubbed Rainbow Six) as an international counter-terrorism force, designed to be nobody and nothing to the media, to work around all the usual red tape, but get the job done for the sake of the people whose lives are at risk. Clark recruits the best the world's militaries have to offer, taking in highly trained soldiers from around the world and getting them to share a unified vision and tactics where hostage situations and terrorists are involved.
The bulk of the story entails the bad guys gradually realizing the bigger picture of what each other is up to and Rainbow attempting to thwart their every move, while also slowly putting together the pieces of why there's been so much international terrorism lately. It all comes to a head when all three sides become acutely aware of what the other is doing, primarily through good old fashioned Cold War espionage, and alliances change quickly as these three powers go head-to-head.
The first game — simply titled Rainbow Six — focused on re-enacting the action sequences of the book, putting the player(s) into the Nomex-Kevlar shoes of the Rainbow operatives themselves. Realizing that the half-dozen or so encounters in the book wouldn't make for a very satisfying game, some new missions and soldiers were dreamed up to intertwine with those from the actual story, adding some legs and variety to the series, as well as giving more of a hook than simply a book tie-in.
Within a year's time, the game saw two major improvements. The first came in January 1999 in the form of the Eagle Watch expansion pack. This included five new missions (some set in U.S. government buildings), new weapons, and some gameplay tweaks and fixes. Then, nearly a year after the release of the original, the entire game got an overhaul with the launch of Rainbow Six: Rogue Spear. This title featured 18 entirely new missions set all over the world, with a new storyline involving radicals who get their hands on some leftover misplaced nuclear warheads. I wondered where I left those…
In any event, the franchise has generally gotten better with time in terms of visuals and playability, though some of the realism has been sacrificed for the sake of more engaging multiplayer gameplay. It shows no signs of slowing down either, what with planned versions of a new scenario being readied for launch on the PlayStation 3 and Xbox 360 by year's end.