Counter-Strike is a tactical first-person shooter video game developed by Valve Corporation which originated from a Half-Life modification by Minh "Gooseman" Le and Jess "Cliffe" Cliffe. By the fourth beta version, Valve Software, the developer who created Half-Life, began assisting in the development of Counter-Strike. In 2000, Valve bought the rights to Counter-Strike.
The game has been expanded into a series since its original release, which currently includes Counter-Strike: Condition Zero, Counter-Strike: Source, and Counter-Strike: Global Offensive. Counter-Strike pits a team of terrorists against a team of counter-terrorists in a series of rounds. Each round is won by either completing the mission objective or eliminating the opposing force.
The game was the most played Half-Life modification in terms of players, according to GameSpy in 2008.
As of August 2011, the Counter-Strike franchise has sold over 27 million units.
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