The Greys are the overarching antagonists of Resident Alien.
They are a hostile alien species that terrorize, abduct and torture life forms across the universe. They appear to be technologically advanced as they operate spaceships that can freeze time and the living beings inside a specific location.
Harry first mentions the Greys in "Homesick" saying even they won't touch almond milk - implying that Harry looks down on Greys as intellectually inferior to his people but not as much as humans.
Harry again mentions the Greys in "Birds of a Feather" complaining they have an ass fetish shoving things up people's butts.
In "Welcome Aliens", Harry calls the Greys "insidious assholes" and they are a hot topic at the Alien Convention. Harry, looking for a battery to recharge his device at the Alien Convention, finds that a few of the people who encountered aliens have a chip installed in their bodies and mentions to Asta that the Greys input chips into a witness of the abductee or the abductee themselves as part of a migration tracking device. He then gets pursued by Peter Bach, an alien hunter who accuses him of abducting his baby right out of his wife on a bus in New York around the early 1990s until Harry defends his people don't kidnap anyone, that's the Greys. Harry proceeds to extract a chip made by the Greys that was planted in Bach's neck to finally repair his device and make it fully operational again.
- It is likely that the alien ship that General McAllister encountered in her childhood belonged to that of the Greys. The spaceship she saw in her childhood does not match the spaceship Harry was piloting to come to Earth so it was not Harry's people.
- They have yet to appear on the show directly.