4/26/1986 (or if you prefer 26/4/1986)
I know many people here were not even born yet, but this event had a profound future effect on the video game industry, and I don't mean just S.T.A.L.K.E.R. The idea of post-apocalypse in art/cinema/gaming wasn't new when Chernobyl happened but when it did, suddenly there was a place on Earth that was an actual real slice of what a post-apocalypse might be like.
[Blocked Image: http://enformable.com/wp-content/uploads/2015/09/Chernobyl-Trip-2015-013.jpg]
[Blocked Image: http://static5.gamespot.com/uploads/scale_super/gamespot/images/2007/077/reviews/785116-540331_20070319_001.jpg]