The Impostors that give Among Us its name and central gameplay hook are, by design, a mysterious bunch. On the surface, they're nearly identical to Among Us' colorful crewmates, but Impostors exhibit certain strange and terrifying properties. Due to the game's lack of overt story, it's unclear what exactly Among Us' Impostors are, but fans have a few compelling theories.
Unlike normal crewmates, Impostors have the ability to slink through vents, which - unless crewmates are small enough to do this, too, but simply have no need to - suggests they have some kind of shapeshifting ability. This would also explain Impostors' ability to open up a large mouth at the waist of their spacesuits and stab victims with sharp tongues. It's possible Among Us' crewmates also have mouths hidden there, and the Impostor only uses this horrifying ability because of some malicious motive. Since no other crewmates are seen doing this, though, it seems unlikely.
Knowing Impostors possess these unique properties, Among Us fans have naturally tried to figure out exactly what Impostors are and where they came from. Although the exact nature of their biology is hard to determine without clearer statements from developer InnerSloth, there's still much fans can glean about Impostors' intelligence and origins.
Among Us Impostors' Possible Origins Explained
As explained in a theory by Apex Legends YouTuber KEVTHEKING99-YT, the Impostors, whatever they are, appear to have come from Polus, a planet that hosts the Among Us map of the same name. The crewmates' research there seems to have gone wrong, resulting in either the escape of a shapeshifting specimen that mimics crewmates or an infection that turns them into Impostors. Since Impostors leave behind half-devoured crewmate corpses, KEVTHEKING99-YT theorizes they are essentially just animals, attempting to feed and survive through camouflage, as some Earth predators do.
One potential problem with this theory is Among Us' Impostors exhibit more intelligence than traditionally associated with animals. They are able to deliberately sabotage crewmates' tasks and perform their own fake tasks, so they seem to have at least some awareness of the crewmates' goals. Perhaps, then, the parasites or shape-shifters are intelligent creatures. The lengths they goes in order to eliminate entire crews might give more insight into this intelligence, too: Rather than opportunistic hunters looking for a quick meal, Impostors could have a purposeful vendetta against crewmates, attacking them in retaliation for invading their home planet.
One darker theory, from Reddit user I_exist_YaYY, suggests there might not even be a real Impostor. According to the theory, a paranoid crewmate, spurred on by horror stories of a shapeshifting enemy, begins to suspect others are Impostors and secretly kills them in an attempt to protect the crew, thus unwittingly becoming the Impostor themselves. This, of course, wouldn't explain the big mouth, sharp tongue, or half-eaten bodies, but maybe the would-be savior's deteriorating mental state leads them to hallucinate such horrific killings. Still, this theory seems less likely than the others, so it's safer to assume Among Us' Impostors really are some kind of vengeful, alien body-snatchers from Polus.