Of all the movie monsters, the zombie is the most deceivingly simple. Zombies are reanimated corpses, hollow, decayed husks of their former selves driven by primal instinct. Yet, zombies almost always tend to serve as reflections of current fears, making their evolution in film one of the most interesting. In other words, zombie movies are never even really about zombies. From voodoo to viral outbreaks, from rigor mortis crawls to rage-induced sprints, the zombie has grown from B-movie status to mainstream pop-culture phenomena over the decades.

Long before they made their debut on celluloid, the zombie terrorized through Haitian folklore and storytelling. The word “zombie” is said to have come from “nzambi,” which in West Africa translates to “spirit of a dead person,” or “zonbi,” a Haitian Creole word that refers to a dead person that’s been reanimated by magical means. Haitian folklore usually featured Bokors as the necromancers of the dead. These practitioners of the dark arts would resurrect the deceased, though they’d have no free will or speech. They were slaves to the master who raised them. So, it’s not surprising that the first zombies on film followed this tradition in 1932’s White Zombie.

Based on William Seabrook’s novel The Magic Island, White Zombie stars Bela Lugosi as Murder Legendre, an evil voodoo master with a horde of zombie slaves that operate his sugar cane mill. A wealthy plantation owner seeks Murder’s help in luring a woman away from her fiancé, but Murder instead turns the woman into another one of his zombie slaves. 1943’s I Walked with a Zombie follows a nurse hired to care for a Caribbean plantation owner’s ailing wife, and runs afoul of voodoo and zombies. 1941’s King of the Zombies saw a trio of wayward travelers wind up at an island mansion for refuge, and find their host is not only working with spies but a voodoo master of zombies. In Revenge of the Zombies, a Nazi inhabiting an old Louisiana swamp mansion raises zombies to amass an undead army for the Third Reich. The shared themes and similar plot setups among the zombie films of the ‘30s and ‘40s heavily revolve around race and fears of oppression.

By the ‘50s, horror had shifted into its atomic age, the threat of the atom bomb and nuclear war playing a significant role in the fears of the decade. Threats from beyond the boundaries of Earth also played a significant factor. This reflected in the zombie trope. Genre filmmakers retooled what a zombie could be, and moved away from voodoo. Teenage Zombies featured a mad scientist that turns teens into her slaves through nerve gas. A former Nazi controlled an atomic-powered zombie to help a gangster return to power in Creature with the Atom Brain. Aliens resurrected the dead to destroy the living in Ed Wood’s Plan 9 from Outer Space. Aliens flat-out inhabited the bodies of the dead to attack the living in Invisible Invaders.

Richard Matheson’s 1954 novel I Am Legend centered around a sole survivor of a pandemic that wiped out most of the human population and turned everyone else into blood-sucking vampires. The book inspired multiple adaptations, but more importantly, it was one of the apocalyptic movies that inspired the filmmaker who would change how we viewed zombies forever; George A. Romero. His seminal Night of the Living Dead never even uttered the word “zombie,” but created a blueprint that would be copied for decades. His film established that the living dead would devour the flesh of the living, that they could only be destroyed by damage to their brains, and that they could spread their undead status with a bite. Despite the gory nature of these ghouls, they were a faceless foe that revealed that the living were their own worst enemy. The casting of Duane Jones as Ben, the hero that meets a tragic fate at the end of the film for being mistaken as a ghoul, takes on a more socially charged context given the political climate at the time of release.

The blank slate of the zombie outbreak continued in Romero inspired films like Let Sleeping Corpses Lie (The Living Dead at Manchester Morgue), which aimed at counter-culture fears, and Deathdream (Dead of Night) explored Vietnam war anxieties through a fallen soldier’s return from the grave. Romero’s follow up, Dawn of the Dead, aimed its bite at consumerism with its central protagonists barricaded in a mall. Dawn was Romero’s first to actually use the word “zombie” in relation to its flesh-eating corpses.

The golden age of practical effects in the ‘80s meant that zombies as metaphor took a backseat, letting the gore and creature effects take center stage. Lucio Fulci upped the ante on zombie gore with his zombie-centric films. The basic rules of Romero’s Living Dead were mostly adhered to but tinkered with enough to offer up exciting takes on the subgenre. The Return of the Living Dead showed off the dead’s playful side with punk rock attitude. Re-Animator gave H.P. Lovecraft’s work a gory sense of humor with teeth. Dead & Buried reintroduced voodoo to the subgenre. Wes Craven’s The Serpent and the Rainbow eschewed the ‘80s practical effects-driven aesthetic to take the zombie film back to its Haitian roots. Mostly, though, the decade was defined by intricate and unique designs for its brain-hungry undead, with buckets of blood and guts spilled. Peter Jackson’s early ’90s Dead Alive (Braindead) set the gold standard in zom-com gore, though the decade was zombie-lite for the most part.

It was in the 21st century, though, that the subgenre splintered into various branches of exploration of what a zombie could be. Viral outbreak films like 28 Days Later, I Am Legend, and the Dawn of the Dead remake exploited fears of contagion while making the infected zombies faster and stronger than ever before. Zombie comedies like Shaun of the Dead and Fido used zombies as a mere backdrop and catalyst for the personal growth of its human characters. More recently, Train to Busan and One Cut of the Dead used the zombie formula as a foundation to craft heartwarming (and tear-jerking) tales of family bonds tested.

Every time the zombie subgenre falls into an overly repetitive pattern and looks to wane in popularity, a new take brings about a resurgence. Look at The Walking Dead series, for example. Its extreme success didn’t just make zombies trendy again but gave the zombie story mainstream appeal. Even in its latter seasons with viewership at an all-time low, it still pulls in 4.5 million viewers. It also helped pave the way for gore on TV, at least in terms of making it more acceptable.

More than any other movie monster, the zombie has proven adept at evolving; the mindless nature of the living dead makes for a perfect blank canvas. Even without the potential applications of socially-driven horror, we humans tend to fear death and what could be waiting for us beyond. There’s something inherently terrifying about a flesh-eating, rotting corpse, and the apocalyptic nature surrounding it; the not-so underlying message that you can’t escape death is crystal clear.

No matter the ebbs and flows of horror trends, zombies never stay dead for long.