Although zombies appeared in movies as early as 1919, many people credit George A. Romero with setting the standard for modern zombies. In the classic movie Night of the Living Dead, Romero portrayed zombies as slow-moving, flesh-eating corpses, reanimated by radiation from a satellite returning from Venus.
The radiation affected the recent, unburied dead, and the resulting zombies were invulnerable until someone destroyed their brains or separated their heads from their bodies. In Night of the Living Dead, zombies were neither intelligent nor self-aware. They had a very limited use of tools, mostly confined to using blunt objects as cudgels. In Romero’s later work, zombies became somewhat capable of thought, and in some cases self-aware. They still generally moved slowly and had minimal intelligence. Many movies follow the example of Night of the Living Dead and portray zombies as far more dangerous in large groups.
Some recent zombie movies, like Shaun of the Dead, adhere faithfully to the Romero zombie conventions and make frequent references to his work. Others depict faster, more intelligent zombies.
The zombie film has become one of the most versatile of genres – there has been everything from zombie comedies to zombie science-fiction flicks, zombie thrillers, zombie disaster and apocalyptic films, and even romances involving zombies (such as Jonathan Levine’s Warm Bodies (2013)). Sometimes, zombies were also demonically-possessed, or caused by the spread of a deadly virus or plague.
Films like 28 Days Later keep the basic structure of a zombie film but do not portray actual zombies. (In 28 Days Later, people are infected with a virus that takes effect in seconds — they don’t actually die until they eventually starve.)
A few recent movies and games like Zombieland throw all these conventions aside, presenting zombies that move quickly and can think for themselves, much to the chagrin of zombie purists.