The zombies of The Walking Dead are virtually identical to the zombies of George Romero's Living Dead film series: they are human beings that have died and come back to life through unknown means, devoid of humanity and driven solely by an insatiable hunger for living flesh. No explanation has ever been given as to how the dead return to life in either the comics or TV show, though there are a number of theories ranging from a virus, a form of bacteria, radiation and even the wrath of God himself. The closest thing to an explanation on the undead phenomenon is given by CDC researcher Dr. Edwin Jenner, who states that whatever manner of infection causing reanimation is something that every human has already. As such, any person who dies will come back as a zombie regardless of whether they were bitten by a zombie or not. While zombie bites do pass on lethal infections to victims, these are well-known sceptic infections that would normally be fatal anyway and are not the cause of reanimation. The true nature of the zombie phenomenon remains unknown and will probably never be fully explained.
In terms of behaviour, zombies are slow and stupid, possessing no intelligence or memory of their former lives. When prey is near, they will mindlessly shamble towards it regardless of any threats or obstacles. They can be distracted or misdirected by the presence of multiple prey as well as by bright lights or loud noises. They will feed on just about any warm-blooded animal they come across, though only human victims will turn into zombies upon death and the undead plague does not seem to affect any other form of life.
Depending on the situation, zombies can be either very easy or very difficult to kill. They do not feel pain or sense injury and will ignore any attacks against them. The only thing that stops them permanently is damaging the brain; unless the brain is destroyed, even a severed zombie head will remain active, moving its eyes and constantly snapping its jaws.
Zombies have been given a number of names by various different survivors of the apocalypse. For the most part, nobody calls them "zombies" except for a few occasions in the graphic novels. In the TV series, the word "zombie" is never brought up even once. Names for the undead mentioned in both the comics and show include:-
- Dead 'un