Hellhound

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) .

Origin
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, and sent them through to the Aether. Dr. Maxis was teleported to an unknown location, while Samantha was sent to Griffin Station. Samantha seems to now control the Hellhounds as she attempts to kill Richtofen. One of the radio messages hints that Fluffy was pregnant, explaining why there are multiple Hellhounds.

Hellhound Rounds
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.

Black Ops
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.

Black Ops II (Green Run Only)
In Green Run, through a Custom Games lobby, the host has the ability to turn on/off a Hellhound round if the host has selected a Survival or a Grief game mode map. The only maps that are available for Hellhound rounds are Town, Bus Depot and Farm.

DS
On DS, they appear in The House, The Factory and The Overlook.

Trivia

 * If one uses Insta-Kill to kill the last dog of a round, they will not drop a Max Ammo.
 * The Hellhounds have several different appearances just like the zombies. Some are large and intimidating while others look frail and badly burned.
 * The Hellhounds appear every five to seven rounds. The first wave of each party is in rounds 5, 6 or 7, and the others wave are every four or five rounds
 * Hellhounds will attack certain players and do not switch between targets until the one they are after is downed.
 * In Der Riese, there is a door with a warning sign and a Hellhound head nailed to it. On the floor inside of the door, there is a lot of blood.
 * In Der Riese, if a teleporter is near by during a Hellhound round, many Hellhounds will spawn out of the teleporter.
 * Also, on Call of Duty: Black Ops (Nintendo DS), there is no specific Hellhound round. Hellhounds can appear from round five and have increasing likelihood of appearing each round. These Hellhounds will knock down barricades with their teeth.
 * In Der Riese, Dead Ops Arcade and Moon, they can they appear alongside the zombie horde.
 * Hellhounds were originally going to appear in "Five", since there are character response quotes for them in the game's files. This can be seen here.
 * In the game files there is a scrapped audio file with the name mx_dog_wave_b[1 ], suggesting there was to be a song played during the Hellhound round. The song can be heard here.
 * The Temple is the only Call of Duty: Black Ops (Nintendo DS) map that does not feature Hellhounds.
 * A part of "Beauty of Annihilation" plays at the end of a Hellhound round on Der Riese, the Call of Duty: Black Ops version of Shi No Numa and Der Riese, Kino der Toten and Green Run.
 * In Call of Duty: Black Ops II, their eyes remain yellow-orange, rather than blue like the zombies Richtofen controls. This hints that Samantha may still possibly control them.
 * Dempsey snickers "Devil Dogs" at times upon a Hellhound round, a reference to the nickname (supposedly given by the German military) of the U.S. Marine unit he was a part of during the Battle of Belleau Wood, according to his letter.
 * Using PC mods on Call of Duty: Black Ops, it is possible to obtain the weapon dogs use to attack. When used by a player it appears to be a floating TNT plunger and a pink box in the right hand. [2 ] It is referred to as dog_bite_zm. The map will crash if the weapon is dropped.  [3]