Begun as a way to compete with EA's Medal of Honor series, Activision's Call of Duty shooter franchise has now become one of the biggest in the game history. This week Activision announced that it has now received over $3 billion in revenue from all the games in the series since it began in 2005 with the PC-based WWII shooter.

Activision says the series has now sold a total of over 55 million units worldwide. While developer Infinity Ward launched the series, it has now spread to another developer Treyarch. Recently word got out that a third unnamed developer team is now working on games for the series.