They aren't actually dead. That’s the first thing you have to realize about the The Last of Us zombies. In almost every other piece of media, from Night of the Living Dead to Resident Evil, a zombie is a reanimated corpse. But Naughty Dog did something much more unsettling. They took a real-life biological horror—the Ophiocordyceps unilateralis fungus—and simply asked, "What if this jumped to humans?"
It’s terrifying because it’s grounded.
When you’re playing the game or watching the HBO show, you aren't looking at a supernatural curse or a laboratory "T-virus." You're looking at a host. A victim. The people infected by the Cordyceps brain infection (CBI) are technically alive while the fungus threads itself through their muscle tissue and replaces their thoughts with a singular, primal drive to spread spores. If you listen closely to the whimpers of a Runner, you realize they’re trapped inside their own bodies. It’s a loss of agency that makes the traditional "braaaaains" trope look like a Saturday morning cartoon.
How the Last of Us zombies actually function
The lifecycle is what really sets them apart. Most games give you different "enemy types" just for gameplay variety. In this universe, the variations represent time.
A Runner is someone who just turned. They still look human. They can still see. But they have this frantic, twitchy energy because the fungus is overstimulating their limbic system. They run at you because their bodies are basically being piloted by a parasitic nervous system that doesn't care about the host’s long-term survival.
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Then things get weird.
After a year, you get Clickers. This is where the The Last of Us zombies become iconic. The fungus has literally split the skull open from the inside out. Since they’re blind, they use echolocation. That clicking sound isn't just a spooky noise; it’s a biological necessity. It’s incredibly effective world-building because it changes how the player interacts with the environment. You aren't just managing ammo; you’re managing sound.
The science of the real Cordyceps
Neil Druckmann and the team at Naughty Dog famously drew inspiration from a Planet Earth segment. In the real world, Cordyceps targets ants. It compels the ant to climb to a high point, grip a leaf with its mandibles, and die. Then, a stalk grows out of the ant's head to shower spores down on the colony below.
In the fiction of the game, the fungus mutated. While the real-world fungus can't survive human body temperatures, the "Last of Us" lore suggests that global warming forced the fungus to adapt to higher heats. Once it could survive a fever, humans were back on the menu.
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Bloaters, Shamblers, and the "Rat King" anomaly
If an infected person survives for years—usually in a damp, dark environment—they become a Bloater. These things are tanks. They’ve developed thick plates of fungal "armor" that can tank a shotgun blast. They’re also walking biological bombs, throwing sacs of mycotoxin that burn the skin.
Part II introduced the Shambler, which is sort of a regional variant found in wet climates like Seattle. They don't bite as much as they just cloud the air with acidic spores. It's a nasty bit of evolution that shows the fungus is constantly adapting to its surroundings.
But we have to talk about the Rat King.
Found in the basement of a hospital in Seattle, this thing is a nightmare of "Patient Zero" proportions. It’s a mass of multiple infected humans fused together by twenty years of fungal growth. It shouldn't exist. It’s an anomaly. It represents the absolute limit of what the Cordyceps can do to the human form when left undisturbed in a perfect breeding ground. It’s less of a zombie and more of a localized ecosystem of decay.
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The spore problem: Show vs. Game
One of the biggest debates among fans is how the infection spreads. In the games, The Last of Us zombies release spores when they die in enclosed spaces. If you see a corpse stuck to a wall with mushrooms growing out of it, you put on a gas mask. Simple.
The HBO show changed this to "tendrils."
Craig Mazin, the showrunner, argued that spores would be too hard to manage in a live-action setting—everyone would just wear gas masks 24/7, and you’d never see the actors' faces. The tendrils create a "hive mind" connection. If you step on a patch of fungus in one part of town, the horde a mile away feels it. It adds a layer of tension that the game didn't have, making the environment itself a silent antagonist.
Why this matters for the genre
The brilliance of these creatures is that they aren't the main point of the story. They are a catalyst. They are a force of nature, like a hurricane that never ends. By making the The Last of Us zombies biologically plausible, the creators forced the characters—and the audience—to focus on the morality of survival.
When a zombie is just a monster, killing it is easy. When a zombie is a person whose mind has been hijacked by a real-world fungal parasite, and you can hear them crying out between snarls, the violence feels heavier. It stays with you.
What you can do next to master the lore
If you're looking to dive deeper into the biology or the gameplay strategies for dealing with these threats, there are a few specific things worth doing.
- Watch the original Planet Earth 'Cordyceps' segment. Seeing the real-life "zombie ant" in action makes the game feel ten times more grounded and terrifying.
- Listen to the 'The Last of Us' Podcast. Specifically, the episodes featuring Craig Mazin and Neil Druckmann where they discuss the transition from spores to tendrils and the biological logic of the Bloaters.
- Play the 'No Return' mode in The Last of Us Part II Remastered. It’s a roguelike mode that forces you to fight different stages of the infected in randomized encounters. It's the best way to learn the specific "tells" and sound cues for each stage of the infection without the pressure of the main story.
- Read 'The World of the Last of Us' art book. It contains detailed anatomical sketches of how the fungus attaches to the human skeletal system, which explains why Clickers move the way they do.