Call of Duty Zombies fans recently took a trip down memory lane, digging through old discussions about the game that started it all, Call of Duty: World at War. The legendary FPS from now-longtime Call of Duty developer Treyarch ushered in a new age for the series, placing players in the middle of World War 2. Along with multiplayer and campaign modes, Treyarch also included a secret Zombies mode in World at War that has since grown into a massive franchise.