GSC Gameworld is trying to do what George Lucas couldn't – make a prequel that is a compelling answer to questions people have about the elaborate world that they have created. S.T.A.L.K.E.R: Clear Sky takes place one year before the events in the original S.T.A.L.K.E.R and is intended as a gap filler.
"There are a lot of white spaces in the S.T.A.L.K.E.R universe," explains PR manager Valentine Yeltyshev. "Fans and critics had a lot of curiosity about this place." So, GSC has cast you as a mercenary S.T.A.L.K.E.R, opposed to the hero from the first game, just so you can get a better grip on their alternate post-Chernobyl scenario.