From Wikipedia
The company was formed in Kiev, Ukraine It was founded by people who split off from GSC Game World a year before the release of S.T.A.L.K.E.R.: Shadow of Chernobyl, in particular Oles' Shyskovtsov and Oleksandr Maksymchuk, the programmers who worked on the development of X-Ray engine used in the S.T.A.L.K.E.R. series. They developed the 4A Engine for Metro 2033.