Alan Tudyk largely gets to play Harry Vanderspeigle in his human form in Resident Alien cast look at Harry and see a human face, but some get an unfettered view of his alien visage. The latter is not a common occurrence, and it all comes down to a specific piece of worldbuilding by the sci-fi dramedy.

After beginning in 2021, Resident Alien quickly became one of Tudyk's Disney characters. Resident Alien's main character is a foul-mouthed extraterrestrial who isn't afraid to turn violent when it's required of him. While he eventually developed into a more traditional protagonist, there's still a lot that's unique about Harry - including how he's perceived by those around him.

Some Resident Alien Characters Have A Specific Genetic Mutation

Resident Alien's alien-spotting ability is very rare

In Resident Alien's very first episode, Harry is disconcerted by the ability of Judah Prehn's Max Hawthorne to see Tudyk's character in his alien form. Luckily, no one else believes Max, as they look at Harry and see him as human. Harry's voiceover quickly explains that one out of every million humans has a specific genetic mutation that allows them to see past his "molecular reconstruction​​​​​​." It just so happens that one of those humans happens to live in Patience, Colorado.

Despite a couple of attempts by Harry to kill Max so he can remain undetected, the pair eventually develop an uneasy alliance that almost borders on friendship - but not quite. Unfortunately, Harry encounters another human that shares Max's mutation - Terry O'Quinn's Peter "The Alien Tracker" Bach. After a short time as enemies, Harry and Peter also eventually settle into a healthier dynamic.

Harry Isn't The Only Alien Exposed By Max & The Alien Tracker's Ability

Heather is one of the other Resident Alien characters whose disguise can be compromised

Harry isn't the show's only alien. That being said, other beings from beyond the stars don't show up all that often. When they do, it's not even a certainty they'll be in disguise - as proven by the Grey Aliens. However, other Resident Alien characters do hide behind a human veneer. For instance, Edi Patterson's Heather looks every inch the Blue Avian she is when Max looks at her.

Whenever a character with the mutation is in the scene, characters like Harry and Heather tend to be shown in their alien form.

Similarly, the Mantid - introduced at the end of Resident Alien season 3 - also boasts the ability to shapeshift. Thankfully, this skill is proven to be rendered inert by Max's mutation. Despite attempting to live in disguise as Harry's human appearance, Max knows it's really the Mantid. Other alien characters are such a rarity in Resident Alien that it's easy to forget that the genetic mutation is essentially universal across all alien life, but that is the case.