Zombie

Zombies are deceased humans that have been reanimated and are the primary antagonists of the Zombies and Exo Zombies game modes. They also appear in the Call of Duty: Advanced Warfare gametype Exo Survival as a bonus wave on the map Riot. In the original Zombies mode, they are created by Element 115, and in Exo Zombies, they are the product of an Atlas program gone wrong.

Creation
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 was caused by Element 115, an element found in meteors that 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, Call of the Dead, and Shangri-La. Meteors can also be seen on the Moon whenever it is visible.

The earliest sighting of zombies was in France, during the First World War, sometimes between 1917 and 1918, where the Germans first uncovered Element 115. However, zombies have existed since the Middle Ages, as seen by the Templar Zombies found in France.

While working with Element 115 to power new weapons and the teleporters, Dr. Ludvig Maxis, a German scientist, discovered it could also reanimate dead cells and created an undead army. Unfortunately, this army could not be controlled as the zombies would always go berserk when tested. Edward Richtofen, Maxis' assistant, believed Maxis was not 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.

In Call of Duty: Advanced Warfare, they are created by a Manticore strike. In the intel from Bio Lab, Irons states that Manticore has a second effect to regenerate cells that are possibly dead, but this was unconfirmed.

Hellhounds are dogs that appear in all Zombies games, both as a special type of enemy separate from normal zombies. They are a vicious and murderous type of enemy that appears on Shi No Numa and Der Riese on Call of Duty: World at War as well as appearing on Call of Duty: Black Ops in Kino der Toten, Dead Ops Arcade, Moon, on Call of Duty: Black Ops (DS) in House, Facility, Overlook, Call of Duty: Black Ops II in Green Run maps (in customizations of private match) . A rumble of thunder and an ominous guitar note will be heard at the start of a Hellhound round, as well as the Demonic Announcer saying "Fetch me their souls!" (at the start of the round on Call of Duty: Black Ops, and after the first Hellhound spawns in Call of Duty: World at War).

On these rounds, the arena becomes foggy. They are the puppies of Fluffy, Samantha's pet dog who Richtofen and Maxis turned into the "Original Hellhound". They possess the ability to teleport (but only use it to appear on the map), and they appear with a bolt of lightning marking where they spawned at. The ground rumbles when a Hellhound has spawned nearby. They are weaker in terms of attack power and health than normal zombies, but are also much faster and may spawn anywhere on the map, rather than fixed positions.

After round 16 on Der Riese, Hellhounds spawn at the same time but also still get separate rounds where they appear alone. When the last Hellhound of the round is killed, it will drop a Max Ammo power-up. When a Hellhound round ends in Der Riese and Kino der Toten, "Beauty of Annihilation" is heard. The same goes for Pentagon Thief rounds in "Five" and Space Monkey rounds in Ascension. "Five" and Kino der Toten, both from Call of Duty: Black Ops, feature a new kind of zombie called Crawler Zombies. The Crawler Zombies is a zombie that crawls on all fours (hands and feet). It emits an "aura" of Nova Gas upon death, unless it is killed by a Ray Gun, Thundergun, explosives or melee weapons. Apparently, the Crawler Zombies were a failed experiment by Maxis, according to Richtofen.

In Call of Duty: Black Ops (DS), they look less fluffy and are not on fire, but still look badly burnt. They do not come on their own round; they come in with other zombies after opening the first door on the map.

Ascension features its own exclusive "special round" enemy, the Space Monkeys. Space Monkeys are monkeys from the Soviet Union's Space Program that came into contact with Element 115 when they were sent to the moon. In-game, they appear in the same manner as the Hellhounds that they replaced, there is a misconception that in order for them to be able to appear, the player(s) would have to have the power turned on, and that one player has to have a perk. When a Space Monkey round begins, the map turns into a yellowish-color for a moment, then the map turns dark-orange, with an alarm buzzer being heard, and the cosmodrome's announcer saying "Warning, thief entry detected. All security personnel on high alert." Space Monkeys will appear and try to steal the player's perks by jumping onto and attacking the Perk-a-Cola machines. If the player is too close to a monkey, it will jump, and upon landing, releasing gas that impairs vision and movement. They can also damage the player directly. If they are all killed before they can even touch a perk machine, they will drop a Max Ammo and the Random Perk Bottle power-up, which gives the player a free perk.

In Call of the Dead, George A. Romero appears as a "special guest" boss zombie that follows the players around. He will continually follow players until he is killed. He is very difficult to kill due to his extremely high health, and when he is shot (or he hits a player) he will go into a "berserk" state and sprint after players when he is hit, although the water areas can be used to calm him down by running into them. Insta-Kill and Nuke power-ups are completely useless against him, and he will simply laugh when hit by a Nuke. He can also emit a special yell that causes all zombies in the vicinity to go into a very fast sprint, a feature not seen since Verrückt. Nearby zombies can absorb the electricity emitted from the stage light that he carries around as a weapon, and use it to stun the player upon contact. When he dies, he will drop the Death Machine and the Random Perk Bottle power-ups. If the player that killed him has performed the Original Characters Trapped Easter egg, he will instead drop a Lightning Bolt power-up, which when grabbed, is actually the Wunderwaffe DG-2. However, he is not permanently dead, and he spawns again after two rounds (including the round when he was killed).

In Shangri-La, zombies are citizens, female zombies also appear for the first time. Zombie Monkeys appear for the first time and enter the map when a power-up appears. They then take the power-up and randomize it on their back. They must be killed before they leave the map or the player will lose the power-up. If the player takes the power-up when the monkey is going for it, the monkey will chase and hit him before leaving. Two other zombie types also appear in Shangri-La: the Napalm Zombie and the Shrieker Zombie. The Napalm Zombie walks extremely slow and will kill zombies in his path to reach the player. When he reaches a player or is killed, he explodes and leaves a patch of Napalm where he was. Shrieker Zombies run extremely fast and will try to blind the player when they reach them. If they're killed while screeching, all of the surrounding zombies will be killed along with it.

In Moon, the Crawler Zombies have further mutated into Phasing Zombies, which are able to teleport short distances at fast speeds. Astronaut Zombies also appear having high health and special abilities. When they reach a player, they will teleport him/her and steal a random perk from them. When killed, they explode and push the players backwards.

In House, Overlook and Facility, the zombies are of unknown nationality. Their eyes glow red, similarly to the zombies in Dead Ops Arcade and Mob of the Dead. It features the return of Hellhounds, although they look less hairy and are not on fire. They also don't appear on their own round; they come with normal zombies. You have to open the first door for them to start coming.

In Temple, the zombies are Vietnamese soldiers. They act the same as the ones from the other Call of Duty: Black Ops (DS) maps. They retain the red eyes like the zombies from the other maps, too. Unlike the other Call of Duty: Black Ops (DS) maps, it does not have Hellhounds.

In Green Run, Nuketown Zombies, Die Rise, and Buried, the zombies have now gotten more numerous and now have blue eyes due to Richtofen's control (Richtofen switches souls with Samantha and becomes demonic announcer at the beginning of round 25 in Nuketown Zombies). Die Rise introduces Jumping Jacks; zombies with a similar appearance to Crawler Zombies, appearing in their own round and jumping off walls in an unpredictable manner. It also adds zombies which have armor that gives them extra health. This extra health is only really noticable on rounds 1 & 4; it takes 2 knife slashes to kill a zombie on round 1, and 4 slashes on round 4.

In Mob of the Dead, the zombies now have red eyes due to the map taking place in Purgatory, meaning the "zombies" in the map could be more demonic in nature. Brutus is also featured; a large, heavily armored zombie with the ability to lock down several of the map's utilities.

In Buried, zombies are now dressed in American western attire, such as cowboys, prospectors and barmaids. The traditional blue eyes return, as the map is set during Richtofen's control, however should the player choose to follow Maxis in all three Easter Eggs the eyes will glow orange, as Maxis gains control of them. A new boss, the female Ghost, appears in the level, though she is not actually a zombie.

In Origins, the zombies return to the classic yellow eyes, as it is explained in-map that Samantha is once more in control of them (through whenever it is the same Samantha that talks to the players or a younger version is not fully explained). However, the Crusader Zombies have white or purple eyes, with the most popular and accepted theory being that they do not listen to any Demonic Announcer and simply act on primitive survival instincts. This would make sense, seeing as they would have been zombified long before the ancient ruins were discovered. Templar Zombies also make an appearance in this map, as a hinderance to the player, these zombies target the 115 Generators that the player needs to provide power. Yet another 'special zombie' appears in this map, called the Panzer Soldat.

Special Zombies
While zombies exhibit a variety of features and behaviors depending on their location, some formerly-human undead prove to be an almost entirely different monster. There are even some that were not human to begin with.

The zombie variants include:
 * Hellhounds
 * Crawler/Phasing Zombies
 * Pentagon Thief
 * Space Monkeys
 * George A. Romero
 * Zombie Monkeys
 * Napalm Zombies
 * Shrieker Zombies
 * Astronaut Zombies
 * Denizens
 * Avogadro
 * Jumping Jacks
 * Brutus
 * Ghosts
 * Templar Zombies
 * Panzer Soldats

Speed
The zombies have varying speeds and movements, and some are exclusive to certain maps. These speeds are:


 * A slow stumble with arms by their sides.
 * In Shi No Numa, zombies might stumble around in a sort of sideways manner with arms by their sides and with their shoulder tilted towards the player.
 * The Nazi zombies on Verrückt, Der Riese and Kino der Toten may occasionally Goose Step march when walking up to a barricade.
 * A normal walk with their arms waving in the air and their faces glancing upward at the sky.
 * A jog with arms straight out, like a stereotypical zombie.
 * A fast run. Their arms move back and forth, similar to a human.
 * A sprint, with one arm in front of them pointing down and the other behind them in the air.
 * In Verrückt, Call of the Dead,  Moon, and Origins, some zombies have a human sprint-like speed with their shoulders forward and arms moving as a person would while running (although to less of an extent). These are considerably faster than any other speed, and run at roughly the same speed that the player does with a high-mobility weapon (without sprinting). The sprinting zombies on Call of the Dead are running more human-like than sprinting zombies from Verrückt. Any gun class other than a high-mobility weapon will require the player to sprint in order to not get caught by them. In Call of the Dead, zombies are brought to this speed by a special yell from George A. Romero, but in Verrückt, they will merely spawn sprinting. In Moon, however, they will begin to sprint after the player once they are launched by the Gravity Lifts. This also causes crawlers to quickly scramble towards the player on its hands and knees (even when both legs are missing). In Origins, zombies are brought to this speed by running after the Tank in a similar fashion to the bus in Green Run. However, the animation for running is the same as the Call of the Dead sprinting zombies. Note that if a zombie catches up to a player on the tank, they will continue sprinting, which may be frustrating to most players, especially ones who do not have the Juggernog perk.
 * In Ascension, zombies sometimes crouch down and perform a roll towards the player, or maybe even sidestep to avoid getting hit. When they sidestep they appear to lose their balance and slow down to a slow walk before they finish sidestepping.
 * In Moon, when outside on the surface, zombies float around a lot due to the gravity.
 * In the Call of Duty: Black Ops (DS) maps, they walk with their arms out for the first few rounds, then start to sprint with their arms to their sides, like the zombies in Zombie Verrückt.
 * In Green Run, zombies that are chasing the bus will sprint extremely quick, faster than in any previous map.
 * Zombies inside or on top of the bus in Green Run will slowly stumble to the left and right towards the player due to losing their balance while the bus is moving. Oddly, even when the bus is not moving, they still walk sluggishly in the same fashion as if it were still moving.

Behavior
Zombies will only attack a player through melee attacks; they do not use weapons. Zombies can be gibbed, but will continue to attack the player even after having lost half of their limbs. Note that in-game, it is impossible to destroy a zombie's legs so that it will be forced to crawl if it is already missing an arm. Zombies will not continue to attack players who have been downed, instead continuing onwards to the next player as if the one who has been downed is not there.

Zombies typically chase after the closest player, and can be distracted by either approaching or attacking them. Alternatively, a Monkey Bomb or a human who has been "turned" by the V-R11 will serve to divert their attention for a short time. Also, the Pack-a-Punched Crossbow, the Awful Lawton, acts as a distraction weapon.

In both Call of Duty: World at War and Call of Duty: Black Ops, zombies retain some vestiges of human behavior and intelligence. They are capable of limited speech, including shouting the words "Sam" when attacking the player, or "Monkey" when presented with a Monkey Bomb. Also, the Nazi zombies sometimes appear to march, and the Russian Zombies from Ascension will sometimes roll or sidestep to avoid being shot, a Spetsnaz battle maneuver.

According to George Barkley, humans who are in the process of becoming a zombie suffer from short-term memory loss, psychosis, delusion, and paranoia.

Health
The health of zombies increases with every round. Zombies start with 150 health on Round 1, and gain 100 health every round until round 9. Upon reaching round 10, their health is given a 1.1 multiplier every round.

For example, a zombie has 550 health on Round 5, 1045 on Round 10, 2710 on Round 20, 47295 on Round 50 and 5552108 on Round 100.

Damage Multipliers
With any weapon, damage is applied to zombies. A head or neck attack will multiply weapon damage by 2.0, a chest or torso attack will multiply weapon damage by 1.5, and a limb or groin attack will multiply weapon damage by 1.0.

Call of Duty: Advanced Warfare
Zombies in Call of Duty: Advanced Warfare are different than the zombies of Treyarch's Zombies mode. Their first appearance is in the final wave of Exo Survival on Riot. The player is notified of a Manticore launch and the map becomes covered in fallout waste, and then zombies begin to attack the player. These zombies are fast but have low melee damage compared to the ones in Treyarch's Zombies mode. They can be killed with a few shots from any weapon. Some zombies wear Exoskeletons and can use the boost ability; they might even throw grenades back at the player. The players must survive until extracted by a Warbird. Completion of this wave rewards the player with a zombie character and armor for multiplayer.

Zombies also appear in the game mode Exo Zombies. They look and act more like the zombies from Treyarch's Zombies mode than the zombies in Riot. Some differences, however, include that they do lower damage, some have special powers, and more parts can be gibbed off at once.

The Exo Zombie variants include:
 * EMZ
 * Charger
 * Exploder
 * Security Dogs
 * Hosts
 * Goliath Exo Zombie
 * Acid Dripper

General

 * The player can equip the melee weapon the zombies use (appropriately named "BRAAAINS...") using the console commands.
 * Any headless zombie will continue to take damage every second until they die, upon which the full 100 points for the headshot is awarded. Furthermore, any form of attack will kill it in one hit.
 * If a zombie cannot hit a player in a certain amount of time, the zombie dies, allowing another zombie to spawn.
 * Zombies' heads will explode upon the end of the match. The same can occur to a zombie if one needs to spawn elsewhere during a match.
 * The color that glows in zombies' eyes changes depending on the Demonic Announcer controlling them at the time: blue for Edward Richtofen, yellow for Samantha, orange for Ludvig Maxis and red for an unknown entity (as seen in Dead Ops Arcade and Mob of the Dead).
 * In Der Riese (including World at War), Black Ops and Black Ops II, beginning with Round 4, the last zombie of a round will start sprinting. In Call of Duty: Black Ops, it initially goes with its normal speed until aggravated while in the other games it starts sprinting as soon as the second to last zombie is killed.
 * A few of the zombies' voice clips were used as a sound effect for a Halloween decoration called 'Possessed Wall Hanger'.

Call of Duty: World at War

 * If a grenade is thrown at a zombie that is about to come out of the ground, it will go into a crouching stance.

Call of Duty: Black Ops

 * On the Nintendo Wii version, the zombies' voices are higher in pitch.
 * In Call of Duty: Black Ops (DS), sometimes when knifing a zombie, there will be a delay before they die.

Call of Duty: Black Ops II

 * A zombie can be seen on top of a balcony in the non-canonical ending of the campaign, while everyone is dancing.
 * Walking zombies appear even during higher rounds, though they become less common.
 * This is not the case in Origins, however.