Zombie's?
Though the origin of the zombies remains mostly unclear, various incidents leading up to the creation of the zombies can be found via radio messages found in various maps. It would appear that element 115, an element found in meteors and known to power Wonder Weapons, can reanimate dead cells. A meteor containing 115 is shown in the map Shi No Numa outside one of the swamp areas. Meteor fragments can be seen on Kino der Toten and Call of the Dead. Meteors can also be seen on the moon whenever it is visible.
While working with element 115 to power new weapons and the teleporters, Dr. Maxis discovered it could also reanimate dead cells and created an undead army. Unfortunately, this army couldn't be controlled as the zombies would always go berserk when tested. Richtofen believed Maxis wasn't acting quick enough and decided to betray him to further the research.
One day, Maxis used his daughter Samantha's dog, Fluffy (who was pregnant), as a test subject for his teleporter. Unfortunately something went horribly wrong and Fluffy transformed into the first Hellhound. After this event his assistant, Richtofen set his plan into motion when he locked Maxis and Samantha in the teleporter room with the mutated Fluffy, who then killed them.
Later in both "Five" and Kino der Toten, a new zombie called the Crawler Zombie appeared. The Crawler Zombie explodes and emits Nova Gas (which is different from Nova 6, which is far more lethal) when it dies (unless it dies from a Ray Gun or a knife attack). Richtofen says the Crawler Zombies were a failed experiment of Maxis'. The Space Monkeys are primates from the Soviet Space Program that came into contact with Element 115 when sent to the moon.
It was later revealed that Richtofen used Samantha in some of his tests. In Call of the Dead, George A. Romero appears as some sort of boss-zombie after being kidnapped by a zombie during a movie shoot. Why he retains at least a sense of his former self is unknown.
Hellhounds
"Fetch me their souls!" — The Demonic Announcer at the beginning of a Hellhound round. The Hellhounds are an aggressive and murderous type of enemy first encountered on Shi No Numa. They are encountered on Shi No Numa, Der Riese and Kino der Toten. They are essentially zombie-dogs that are believed to be the mutated version of Samantha's pet, Fluffy and her offspring. They randomly spawn throughout the map (a ball of lightning will usually indicate whenever they spawn) every 4 to 7 rounds and their sole objective is to kill the player by streaking towards them and either attacking with tooth and claw or by exploding. The ground shakes whenever they spawn. There are two variants of the Hellhound: the Flaming Hellhound, which on top of being perpetually on fire, explode on death, and normal Hellhounds.
Crawler zombies
Crawler Zombies (called Creepy Crawlers in Dead Ops Arcade) are a special type of Zombie featured in Call of Duty: Black Ops. According to Dr. Richtofen, they are failed experiments. Crawler zombies are not to be confused with "crawlers", a common name for zombies that have had their legs shot/blown off, and crawl toward the player slowly. They are also known as Gas zombies, Nova 6 zombies and the "six".
The Pentagon Thief
The Pentagon Thief is an enemy who only appears on the Zombie map, "Five", and steals player(s) weapons
Space monkey
"Get your hands off me, you damned dirty ape!" — Takeo Masaki after killing a space monkey that attacked him. "At least they're not throwing shit." — Dr. Richtofen when being attacked by a monkey. Space Monkeys are first, and so far only, introduced in Ascension. They are similar to the Pentagon Thief by stealing the players' weapons, except they steal the players' perks in the form of attacking the various perk machines and can also damage the player's health and kill the player. They replace the Hellhounds and Pentagon Thief on this map. They wear space suits similar to the ones worn by regular zombies, and are likely zombified primates from the Soviet Space Program. The space monkeys will attack a perk machine until the player loses his/her perk. Once the machine has been disabled the player must re-buy the perk. If the players successfully kill all monkeys without having any machines attacked then they will drop a random perk bottle at the end of a round, giving the player a random perk. The monkeys arrive in rockets crashing onto the ground. It can be assumed that they are related in some way to Yuri Kravcheski, due to an excerpt from his rant in the second radio message, "My intellect is ill served blasting a bunch of monkeys into the atmosphere!". It can also assumed that they have been exposed to Element 115, due to their glowing red eyes, and increased physical capabilities.
When the monkey round occurs, the player will hear a buzzer in the beginning of the round, and the map will turn in a yellow-orange tint. Also, the announcer will alarm the player by saying "Thief entry detected. All security personnel on high alert.".
It should be noted that if the player has obtained a perk from the random perk bottle and have not opened the area in which the Perk-A-Cola is in, the Space Monkeys will not attack that perk machine.
Cosmic Silverback
The Cosmic Silverback is a zombie silverback gorilla in the Call of Duty: Black Ops zombie map Dead Ops Arcade.
George A. Romero
"Years ago, I did research for a World War II movie. I came across some old Nazi documents. I couldn't believe what I was reading. Element 115, necromancers, raising from the dead, real creepy stuff. The coolest thing is? Some of that crazy shit happened right here." — George A. Romero George A. Romero, stars as a boss-character in the Zombies map Call of the Dead. He is also referred to as "The Director". Romero was doing research for a World War II movie when he came across Nazi documents pertaining to Element 115.[1]