The first known sighting of a Rat King dates back to 1576, when "servants in Antwerp, Belgium discovered seven rats with knotted tails tied together". Now an established phenomenon with multiple cases recorded across the world, but no verified explanation for the cause, Rat Kings have become a staple of folklore horror, inspiring countless storytellers from Stephen King to Alan Moore.
It was thus only a matter of time before Rat Kings started to show up in video games, as most recently exemplified by The Last of Us Part 2, where it became the basis for Naughty Dog's next evolution of its Cordyceps virus. This eldritch abomination of synthesised infected encouraged the studio to push the limits of its body horror further than ever before and, according to those most closely involved with its creation, marked the fruition of a dream (or nightmare) that had been years in the making.
Note: The following article contains major spoilers for The Last of Us 2.
Naughty Dog had actually been in possession of its Rat King for some time before The Last of Us 2. The problem was that it had nowhere to put it. "Even during development of the first game, we were thinking about what two infected stuck together would look like," says Anthony Newman, co-director of The Last of Us 2. "Visually, it was just a really exciting idea."
A few pieces of concept art for the Rat King were sketched during development of The Last of Us, but the beast was eventually sent into dormancy as Naughty Dog struggled to find it a suitable scene within Joel and Ellie's original journey. The Rat King wouldn't re-emerge until several years later, when the studio found itself storyboarding a trial by fire sequence for Abby, The Last of Us 2's second protagonist.
"We wanted Abby to have this really intense thing that she overcomes, because she's kind of on this redemption mission to get the supplies for Yara's arm," explains co-director Kurt Margenau, "and so it seemed like the perfect place for the Rat King. She's gone through all of these trials: Overcoming her fear of heights climbing to the sky bridge, fighting through hordes of infected on the way down, and coming out the other side thinking the worst was over – only to be thrown right into this nightmare boss fight."
Finally, the Rat King had found its home.
Once the core creative team knew that it wanted to develop the encounter as a fully formed section of Abby's story, Naughty Dog's other teams were looped in to bring it to life. That included sound designer Beau Anthony Jimenez, who you can thank for every roar, crackle, and howl that emanates from the series' hordes of infected.
"The only information I had at first was concept art, design prototypes, blockmesh level art, and prototype motion-capture animations," says Jimenez. "It seemed like an exciting but daunting task, requiring a lot of high-level conceptual work and sound design. I knew that if I finished all the other infected sound design first, I could use those assets as layers in my final vocal designs of the Rat King. It wasn't until quite late in production where I went all-out on fleshing it out and finalizing its sound."
Similarly, animation director Jeremy Yates had to consider how such an unholy matrimony of flesh and fungus would behave, studying preserved Rat King specimens to conceptualise one in motion: "While we've never seen one alive, I imagine it's a coordinated chaos of movements. Similar to conjoined twins, they're independent but must learn to coordinate their movement and work together."
With the bones of the Rat King encounter in place, Naughty Dog could begin thinking about how it would introduce this new infected boss to the player, and the best way it could ramp up the fear factor while staying true to The Last of Us' firmly grounded sense of authenticity. That meant Abby's descent into Ground Zero needed to feel organic, not mechanical, and for Jimenez in particular, it demanded a preamble that would continue to mess with player expectations right up to the Rat King's full reveal.
"Initially, the introduction was a jump scare," he says, reflecting on the earliest days of development. "That didn't excite me, because I felt it wasn't enough time to tell the sonic story of the Rat King. I fell in love with this idea that you start to hear something coming in the distance, and that your preconceptions of infected sounds will try to fill in the gaps as to what exactly was approaching."
"A lot of inspiration came from the mutant bear scene in Annihilation, which was why you hear the blood-curdling stalker cries initially. The player may think a clicker or stalker is approaching... but a couple seconds in, the cries pitch down into a rumble, which vibrate objects inside the ambulance with subsonic bellows. I felt that this approach raised the spook-factor to the nth degree."
Jimenez pitched the idea to creative director Neil Druckmann, who naturally approved, before taking it to Yates and his team of character animators, which now had the daunting task of rigging the Rat King's initial assault on Abby in the ambulance. The solution was to get physical, tying three actors together to capture the kinesthetics of the multi-limbed monster.
"To achieve the ultimate capture solution that we ended up using for the game assets, we built a cage on large caster wheels," Yates recalls. "We knew our two actors would need to be incredibly strong and have a lot of endurance for this shoot, so we had [stunt actor] Chris Robbins play the bloater half and pro parkour athlete Jesse La Flair play our stalker."
"Jesse has incredible upper body strength from his parkour athleticism and was able to build in the ravaged dog movement we were looking for. These two actors were joined at the hips again, but the cage held Jesse in somewhat of a hammock that kept most of his body weight off of his arm. This gave him explosive speed with his left arm and allowed Chris, and a number of assistants, to move and swing the cage around very quickly."
The gambit paid off, providing the animation team with the perfect reference point for detailing the creature's every motion. From there, all that was left was making sure this King looked the part for his small screen debut...
"I think Resident Evil is probably the limit for us in terms of how crazy we want to go," says Margenau of Naughty Dog's approach to building its unique brand of post-apocalyptic horror. "The reason that we entertained the idea of these infected fused together is because there's history in our canon of what happens to them when they sit around for a really long time."
"One big reference point for us was Neill Blomkamp's short film, Zygote. If you look at that video, you can see that there's a lot of inspiration there. Inside is another one; the way the monster's arms touch a lot of stuff is just this inherently creepy thing. So we're aware of things like that, but we had to make it our own and do all the extra work that's needed to make it feel real."
Yates also brings up Inside as an inspiration for the Rat King's physicality, revealing that Naughty Dog's animators even added ragdoll physics to the fleshy growths on its back so as to emulate the gelatinous effect that had players shuddering throughout Playdead's 2016 puzzle-platformer. He also points to another titan of pop culture, but not in the sense that you might expect.
"Ironically, Stranger Things Season 3 also dropped in the middle of development and featured a large creature formed from rats, which chased characters around a hospital. We were already pretty far along in production, so it didn't change much, but it did have a very similar vibe," says Yates. "It was at least interesting to see what our finished version could look like."
Jimenez's references, on the other hand, weren't so much drawn from pop culture as they were the animal kingdom. Layering in distorted big cat roars with avian squawks and snake hisses, the unholy mix was concocted to evoke the Medusa-like nature of the Rat King's many infected parts.
What little remains of the Rat King's humanity is buried beneath layers of congealed infected protoplasm, and Jimenez made sure to reflect that in the monster's sound design, too: "I would layer in gargles, gags, and sloppy wet gore sounds to add a sickening realism to the vocal effects. It needed to sound part of the universe, and part of the established infected family."
Anyone who's had the misfortune of fighting the Rat King will tell you that its chosen arena is not a pleasant place to be. A series of dark, narrow corridors that make up just one section of Seattle's 'Ground Zero', the stage for Abby's face-off represents the iterative culmination of a dozen ditched concepts.
"The first layout was essentially an arena where you're shooting a little bit and then running, and then shooting a little bit and running... and it kind of ended up having this very flat interaction," says Newman, revealing that it wasn't until lead designer Richard Cambier proposed "a Hail Mary last minute change that really elevated the quality of the fight from an eight to a ten."
"He had this idea of introducing these pseudo-dead ends, where you're kind of looking around for your exit in a much more claustrophobic space which allows the Rat King to get towards you, and makes for these really narrow escapes," Newman continues. "I remember we begged the environment team at the last minute and I remember them saying 'Okay, you get this one, but only because you asked so nicely!'"
These "loops", as Naughty Dog refers to them, came in the form of rooms made up of circumventable obstacles, such as a pillar or medical table, that Abby could then use to maintain some distance between herself and the monster.
With these established, in addition to several environmental "shortcuts" that allowed both Abby or the Rat King to slip around each other, Naughty Dog realised it had an arena that felt intensely claustrophobic – encouraging players to think on their feet with a heightened awareness of their own vulnerability.
"We were trying to make sure that the monster is always on screen as much as possible, and not having any dead ends that would kill you," adds Margenau, reflecting on the delicate balancing act Naughty Dog had to perform. "It's scary, and always a close shave, but you never feel like the environment cheated you when you die."
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"The challenge was less about making the fight fair and more about making it interesting," admits Newman. "We have all kinds of characters that will fuck you up if they touch you. One of our bread and butter enemies, the clicker, kills you in one hit. So we had to think about what would make this creature something more than just a really tanky clicker that soaks up a lot of bullets?"
The answer, of course, was the split. Halfway through the fight, a "super stalker" attached to the Rat King will splinter off from its host, in a subversive spin on the boss fight trope of a 'second stage'.
After defeating the Rat King, Abby is then forced into a completely different kind of battle with the stalker; an intense game of cat and mouse that Margenau refers to as the sequence's complimentary "dessert fight". Newman reveals that two other critically acclaimed PlayStation exclusives were the key source of inspiration for this progression of events.
"A big part of the split gameplay was actually inspired by the Magni and Modi bossfight from God of War, where you had these two complimentary enemies – one with a fast weapon and one with a big slow weapon."
"The ending fight with the stalker itself was inspired by Eileen the Crow from Bloodborne. I loved how in a game with bosses that were 20 stories high, the most challenging and brutal fight of them all was this person who is the exact same size as you. So that was something we were really interested in: how can we make an infected who isn't massive feel just as deadly?"
Thankfully, Yates' approach to mo-capping the Rat King with three stunt actors had allowed his team to give "each of the fused bodies their own movement", thus making it easier to animate one tearing apart from the other in a plausible fashion. Meanwhile, Jiminez characterised the super stalker's screams with samples of "slowed down falcon and vulture cries to give it a gritty, terrifying tone that sounded almost like a tortured human".
With both the Rat King and super stalker slain, Abby emerges from the other side of the hospital a changed person. She mentions the creature to no one, despite its potential importance for humanity's understanding of the infected. Perhaps she's shellshocked. Perhaps she's worried no one would believe her. Or perhaps she doesn't want to consider the possibility that the Rat King she killed wasn't just an anomalous exception to the rule.
When pressed for more pieces of Rat King lore, Margenau and Newman are hesitant to explain the minutiae beyond what's revealed in the game itself. "There was at some point gonna be a note somewhere that would hint that there were actually more elsewhere," Newman teases, "but that didn't make it in, which leaves it in this weird like pseudo-canon state."
"Even the name, 'Rat King', is not really canon," Margenau adds. "No one ever refers to it as that in the game itself. We debated whether there should be something that names what it is…"
It's here where Newman chimes in, grinning: "But don't you remember, Kurt? There's that line that Abby was going to say as she first starts running away from it; 'Fuck this... Rat... King?!' We had to cut that one for time."
For more, here's all The Last of Us 2 Easter eggs you should look out for in the campaign, or why not watch our full review of the game in the video below?