The zombie in our world is a living dead monster that has become a popular culture icon thanks to films like Night of the Living Dead (which is in the public domain). But it originates from the West African spritualism and belief system of of Voodoo. According to this belief system, a corpse can be reanimated by a powerful wizard, or bokor; it remains under the control of the sorcerer since it has no will of its own. It is said that feeding salt to a zombie will force it to return to its grave.
There is much research into the nature of West African Voodoo and the folklore surrounding the idea of zombies. Zora Neale Hurston, while researching folklore in Haiti in 1937, encountered a woman in a village whom it was claimed was Felicia Felix-Mentor, a woman who had died and been buried several years before.
Decades later, Wade Davis, again researching Haiti, wrote two books presenting the pharmacological case for zombie mythology: The Serpant and the Rainbow and Passage of Darkness: The Ethnobiology of the Haitian Zombie. Davis postulated that the zombie state could be induced by the introduction of two powders into the bloodstream (usually via a wound), coup de poudre (powder strike) and dissociative drugs such as datura, which together would induce a death-like state, leaving the victim totally in the control of the bokor.
Scottish psychiatrist R. D. Laing suggested that mental illnesses such as schizophrenia could be the root of the psychological aspects of the zombie state.