Zombies
Zombies are one of the basic kind of undead. Essentially, they are people who are dead, but haven't stopped moving. The zombie activist Reg Shoe makes a distinction between 'proper' zombies and mere 'old memories on legs', describing the former as aware and goal-oriented. Unlike zombies in most folklore and horror fiction, they are not automatically mindless, but may retain the same personality they did when they were alive.
This personality tends to be obsessive in some way. A zombie can (usually) only be created if there is something more important to it than passing on. In this case, they may be summoned back by a voodoo practitioner, or simply refuse to leave.
If, for some reason, Death is prevented from releasing someone's soul from their body, the result is many aimless zombies. This has, however, only happened once without someone else taking up the role.
The most difficult thing about being a zombie is that the body has actually stopped living. This means bits are likely to drop off unless precautions are taken. It also means thought is required regarding the autonomic processes, as its functions no longer happen automatically.
A zombie can remain active even if its flesh is lost to wear, tear, and rot. Since this is very inhibitive to social acceptance, most zombies apparently use some artificial methods of preservation. Not doing so can result in becoming a "skeleton man." (One, Gak, appears in Last Hero.)
Noted zombies in the novels include: Baron Saturday, Mr Slant, Windle Poons and Reg Shoe.
Read more about this topic: Undead (Discworld)