I Am Legend was originally a book by Richard Matheson in 1954. It featured an air-borne disease that turned people into vampires. It used the apocalyptic theme to address social, ethical, and religious questions, with its twist ending, where the vampires become the normal and the humans become the legend.
Since its inception, I Am Legend has been made into at least three movies (The Last Man on Earth 1964, The Omega Man 1971, and I Am Legend 2007) and influenced many more (Night of the Living Dead and 28 Days Later). Each of these movies attempted to progress the theme and genre, with 28 Days Later being the first movie to introduce the “fast Zombies.”
The Zombie genre can simply provide screams (and laughs) in the vein of standard horror films, or it can use its extreme scenario to address topics that are very close to home. Indeed, the larger Sci-fi genre is known for doing just this, as Eastern religious ideas find their way into Star Wars, critiques of communism appear in Star Trek, transcendental Darwinism is explored in 2001: A Space Odyssey, and human rights issues regarding cloning and genetic manipulation drive the plot of The Island. X-Men directly speaks to racism and social issues, and the television series Heroes raises questions of ethical warfare and national security.