Zombies, in folklore, is a concept that is rooted in the African religion of Voodoo - according to legend, zombies are reanimated corpses that has been bestowed life by a bokor, a practictioner of black magic, once reanimated the Zombies are slaves to the bokor and have no will of their own: existing to do as the bokor commands.
The Zombie of folklore bear little resemblance to their Hollywood counterparts and don't crave human flesh, nor are they often depicted as rotting and decayed - in most accounts a Zombie in folklore is devoid of all emotion, slow-moving and drained of life yet could be mistaken for someone who is gravely ill rather than a walking corpse, often a Zombie in folklore is only revealed as such when a community or relative identifies the person as having been deceased.
Although seen as a fabrication by most mainstream scientists their has been a controversial theory that the folkloric Zombie described above did exist (and may continue to do so) - however they were not walking dead, rather the theory has it that the bokor utilise advanced poison (perhaps from blowfish) to induce a death-like state in their victim that lasts for several days, sufficient time for grieving relatives to bury them and the bokor to exhume the grave and release their "walking dead".
This theory is not accepted by many scientists and regardless of the truth there are still places in the world where stories of Zombies can be found and the fear of encountering (or worse becoming) the "walking dead" is still very real. For this reason, bokor are afforded a great deal of respect.