Call of Duty is a series of war-themed first-person shooter computer games, whose main publisher is the American company Activision. Initially, the games in the series were focused on World War II, while since 2007 they have been set in contemporary reality. The Call of Duty series has been acclaimed by critics and gamers alike, being a spectacular commercial success with over 100 million copies sold by November 2011; as of January 2012, 40 million gamers were using games from the series for multiplayer gaming. ¹⁾