The Walking Dead takes place after the onset of a worldwide zombie apocalypse. The zombies, colloquially referred to as "walkers", shamble towards living humans and other creatures to eat them; they are attracted to noise, such as gunshots, and to different scents, e.g. humans. Humans that they bite or scratch become infected and slowly turn into walkers as well. It is revealed early in the series that all living humans carry this pathogen, so that if they die from any other cause, they will also turn into walkers. The only way to permanently kill a walker is to damage its brain or otherwise fully destroy the body, such as by cremating it.
The series centers on sheriff's deputy Rick Grimes, who wakes up from a coma to discover this apocalypse. He becomes the leader of a group of survivors from the Atlanta, Georgia region as they attempt to sustain themselves and protect themselves not only against attacks by walkers but by other groups of survivors willing to assure their longevity by any means necessary.