In the original Zombies mode, they are created by Element 115 in Exo Zombies, they are the product of an Atlas program gone wrong, and in Infinite Warfare Zombies, they are used by Willard Wyler with the intention of killing four actors for a snuff film.
They also appear in the Call of Duty: Advanced Warfare game-type Exo Survival as a bonus wave on the map Riot, and are playable in Call of Duty: Warzone in the limited-time mode Zombie Royale. Zombies are deceased humans that have been reanimated or infected by various means and serve as the primary antagonistic force of the Zombies, Exo Zombies, Infinite Warfare Zombies and Nazi Zombies game modes. You were wrong.' - Mission briefing for Nacht der Untoten
' You drove them deep into the heart of the Reich.
