Valve acquired the rights to Counter-Strike in 2000.
Counter-Strike began as a Half-Life modification created by Minh “Gooseman” Le and Jess “Cliffe” Cliffe. Its popularity grew rapidly after the first public beta appeared in 1999. Valve then acquired the intellectual property and hired the developers, bringing Counter-Strike into its official game lineup.
The rights acquisition helped turn the fan-made modification into a commercial series. Counter-Strike was released as a standalone retail product in 2000, while Valve continued developing later versions. This date is distinct from the 1999 launch of the original beta and from the 2004 release of Counter-Strike: Condition Zero.