2025: Overpopulation and pollution conspire to breed a new "super-virus", created by chemical-induced mutation of an existing bug and incubated in the vast shantytowns of the underclass. The virus causes vast mutations to the human brain, turning key sections to become anaerobic tissue and allowing other sections to die off. This creates mindless, vicious assailants that continue to attack long after their circulatory and renal systems have shut down. These infected, quickly nicknamed "zombies" due to their difficulty to kill and hunger for living human flesh, spread like wildfire through the overcrowded Earth.
2030: Overpopulation is now the least of humanity's problems, as the zombie plague has now covered 95% of the areas inhabited by humankind. With the last few strongholds of humanity about to fall, the decision is made to evacuate Earth completely. The resources of the remaining population are devoted to creating ships that can hold the survivors for as long as it takes for the zombies to die off. Robotic killing machines are sent out into the wastelands to humanely exterminate the infected, as humanity leaves the world of its birth forever.
2546: A robotic probe is sent back to Earth to determine whether the planet is fit for humanity once more. What it discovers is a terrifying dystopia where the zombie virus has mutated yet again; the zombie survivors have retained their intelligence, and now rule the Earth. Humanity is kept in "breeding pits", enslaved for life and used either for food, or transformed into consumers of human flesh. The robots have all been overwhelmed, save for one. One last hope for the enslaved and exiled humanity, one last hero for the human race...
WALL-E, Zombie Hunter.
...oh, come on. You'd pay to see it.