2008: Call of Duty: Nazi Zombies
An Unexpected Hit
Upon completion of Treyarch's Call of Duty: World at War
, a secret mode unlocks called Nazi Zombies
. Despite featuring a straightforward concept -- players defend a room from onrushing zombies with guns and by boarding up windows -- Nazi Zombies becomes a huge success. Due to Nazi Zombies' popularity, Treyarch releases three separate downloadable map-pack expansions, which also introduce things like flaming canines and monkey-shaped bombs that attract undead Nazis.