Zombie movies such as Shaun of the Dead have been popular with horror fans for many years. While the kind of undead zombie portrayed in Shaun of the Dead and the Evil Dead movies does not exist, Voodoo, the religion that the stories of zombies comes from has occasionally produced a real life zombie. Rather than the person being deceased, zombies are created using a complex concoction of chemicals to cause brain damage and aid in the mind control of the drug cocktail's victim.
The creation of real life zombies began in the practice of Haiti and is linked to the practice of voodoo. Although magic is typically credited with the creation of a zombie, some very real drugs are used to cause the half-living state of the creatures.
American Biologist Wade Davis found that a chemical called tetrodoxin, which is obtained from the puffer fish, was effective in causing nerve paralysis. Another chemical crucial to the creation of a real life zombie is a fluid secreted by a toad native to Haiti called the bufo marinus. A cocktail of other chemicals including datura stramonium were used to aid the paralysis and mind control process that lead to the creation of the zombie. Voodoo sorcerers would administer the drug cocktail to their intended victims and enslave the affected individuals after the revival process.
While zombies may not be the mindless, undead rotting creatures depicted in many horror films, real life zombies are individuals who were buried in their coffins and dug up later. If the victims were left in their coffins too long, the effects of the mind control drugs would be strengthened, but the lack of oxygen caused irreversible brain damage.
Another type of real life zombie that has been hotly debated but not proven is known as the philosophical zombie. The philosophical has no soul, but is capable of consciousness and independent thought.
Proving the existence of the philosophical real life zombie is far more difficult than finding people who have been subjected to the right mix of drugs to make them walking mindless slaves, as souls must first be proven exist. Once souls can be proven to exist, the existence of people without souls must be proven. Even if the philosophical zombie existed as a type of real-life zombie, the philosophical zombie would for all intents and purposes be human with full consciousness until his time of death.
Even if real life zombies are merely people who have been subjected to a drug cocktail and philosophical zombies result in a logical conundrum, film makers will probably continue to entertain moviegoers with the fictional creatures that came back from the grave.
Sources:
Skeptic's Dictionary -- Zombies