According to More Word Histories and Mysteries:
...zombies are believed to possess only the part of the soul that animates the body, for they have been deprived of the aspect of the soul that gives them their individual personality and the ability to make moral judgments.Zombie didn't appear in English til the 19th century in various historical works, but entered popular speech in the early 20th century. William Seabrook wrote a sensationalized memoir of his time in Haiti called The Magic Island and subsequently introduced the American public to zombies in 1929.
So fascinating. All of this information was taken from More Word Histories and Mysteries from the editors of the American Heritage Dictionaries. I'll be adding more for another day!