The modern zombie was created in 1968 with George Romero classic, 'Night of the Living Dead'. This movie created the zombie that we know today from film, video games, and books. It was the first-ever depiction of dead coming back to life and trying to eat the living in mass hordes. Romero wasn't inspired by the Haitian voodoo zombie; he was actually inspired by a vampire novel from the 1950's called, 'I Am Legend'.
Richard Matheson, the author of 'I Am Legend', was attempting to bring the vampire into the modern age with his novel. What he did was he created a biological explanation for vampirism. It wasn't based on some curse or ancient superstition, it was a bacterial infection. Then what he did, is rather than having vampires be just a single solitary ghoul that lives on the edge of town and eats a virgin every once in a while, he turned vampires into roving hordes that wanted to suck the blood of every last living person on the planet. Sounds a lot like zombies, right?
14 years after 'I Am Legend' was published, a young filmmaker in Pittsburgh wanted to make his first feature film, and he essentially wanted to make 'I Am Legend'. He couldn't get the rights to it, it had already been turned into a movie, and he didn't want to get sued. What he said was, "I'm going to change the creature in 'I Am Legend' just enough so that I can't get sued." He took out any last vestige of vampirism from them. Rather than just having them go out at night, they can go out during the day. Rather than having them be afraid of crosses, holy water, and garlic; get rid of all that stuff. Then the last thing he did is he said, "Rather than having my horde want to suck the blood of every last living person, I'm going to have them eat the whole body, that way nobody can possibly sue me." He thought he was creating a brand new monster that he called the Flesh Eaters.
Romero created what he believed was a brand new monster, and the modern zombie was born.