Call of Duty is a long-running first-person shooter video game series developed by various studios under Activision. It originally focused on World War II settings but later expanded into modern warfare, futuristic combat, and battle royale experiences. Known for its fast-paced multiplayer, cinematic single-player campaigns, and the popular Zombies mode, Call of Duty has become one of the best-selling video game franchises of all time. It releases new titles annually, with Black Ops and Modern Warfare among its most popular sub-series.