Guerrilla Games is a Dutch first-party video game developer based in Amsterdam and part of SIE Worldwide Studios. The company was founded as Lost Boys Games in January 2000 through the merger of three smaller development studios as a subsidiary of multimedia conglomerate company Lost Boys, and was renamed to Guerrilla Games in 2003 before being purchased by Sony Interactive Entertainment in 2005. It is best known for the Killzone and Horizon game series.