G.I. is the name given to the Generic Infantry in the Rogue Trooper universe. The name is a play on the original World War II G.I. They were developed by Souther scientists in a bid to create a genetically modified supersoldier. Because of the widespread use of powerful NBC weapons, Nu-Earth had become toxic and conventional troops were weighed down by environmental suits. To overcome this the scientists create a soldier who was immune to virtually every known toxin and noxious agent known - the G.I. Rogue Trooper (and therefore presumably other G.I.s):-