Since the mode made its debut in Call of Duty: World At War, Call of Duty Zombies has been one of the most popular aspects of modern CoD, with the mode being implemented in almost every instalment of the franchise since 2008. Time and time again, fans have returned to the game's Zombies mode, whether that's to follow the story of the Ultimis and Primis crew or simply to blast their way through hordes of the undead.