Long story short, zombies were created by a group called 935 by German scientists. They were made because people wanted super soldiers. That was back in the 1940’s. Dr.Rictoffen was an assistant of Dr.Maxis (head in charge). One day while they were experimenting on creating a teleporter when Samantha’s (Maxis’ daughter) dog got in it and teleported. Later it came back a zombie and Rictoffen trapped Maxis and Samantha in the teleporter with it. They both teleported and Sam became the leader of the zombies. In Black Ops 1 the Easter Egg on the map Moon is Rictofen switching bodies with Sam so now he is the leader. The zombies eyes turned from yellow (while Sam was the leader) to blue meaning that Rictoffen is in charge. Later in the Easter egg Maxis launches 3 rockets at Earth thus making it have lava everywhere and destroying chunks of it. In BO2 the story continues with the 4 survivors in TranZit, Marlton, Misty, Samuel and Russ man.
More Zombie story line coming soon.