In the Siege universe, there is a special task force named Team Rainbow or just Rainbow. Founded in 1999, Rainbow is a special counter-terrorism unit that operates NATO supervision. The team is made of operators from real life counter-terrorism units (CTUs) and some fictional CTUs. Since it was formed, Team Rainbow has thwarted many terrorist plots but has since been deactivited in 2012. Three years later, a terrorist group that goes by the name, White Masks, has risen to the point that convinced the director of Rainbow, codenamed "Six", to reactivate the team. Now back, Team Rainbow works hard to combat the White Masks, recruiting new operators from around the world.