The Irkens of Invader Zim: The Almighty Tallest, PAKs, GIR and Operation Impending Doom

Invader Zim premiered on Nickelodeon on March 30, 2001, created by the comics artist Jhonen Vasquez, and its aliens were the most fully designed the network had aired. The Irkens are a species of small, green, earless humanoids with antennae, large red or purple eyes and no visible nose, who have built an interstellar empire on a single organising principle: the tallest Irken rules. Two of them at a time, the Almighty Tallest Red and Purple, command from a vast ship called the Massive, and they run their empire the way tall bullies run a playground, eating snacks, mocking subordinates and sending invaders to planets they have no plan to use. Conquest proceeds by Operation Impending Doom, in which each invader is assigned a world, infiltrates it in disguise, and prepares it for the armada.

Zim, voiced by Richard Steven Horvitz, is the empire's shortest and worst invader. Banished to a food-service planet after ruining the first Operation Impending Doom, he crashes the launch of the second, and the Tallest, to be rid of him, invent an assignment on a planet at the edge of their map, which turns out to be Earth. Zim arrives, builds a house with a flimsy disguise and a base underneath it, enrols in a school as a child with a skin condition, and begins a conquest that the series treats as hopeless from its first minute. His only opponent is Dib, a big-headed schoolboy paranormal investigator whose sister Gaz would rather play video games and whose classmates would rather not know.

An Irken is largely a life-support system for a machine. The PAK on each one's back holds its memory, personality and organs' worth of support, deploys mechanical legs, weapons and tools, and cannot be removed for more than ten minutes without killing its owner; Irkens are grown in tubes, plugged into a PAK at birth and told their job by it, and an Irken's life is the PAK's programme. The body around the PAK is built for planets other than ours. Earth's water burns Irken skin, meat burns it worse, the atmosphere gives Zim a rash and the food does unspeakable things; the show's running gag is that the invader's disguise, a wig and contact lenses, fools every human, while the planet itself is trying to kill him.

The Irkens are also a satire of empire that children could follow. Their army is enormous and pointless, their leaders are cruel and bored, their soldiers compete for promotion by growing, and their conquests are catalogued and forgotten; Vasquez drew them as the fascist bureaucracy of a sci-fi serial and let the animation, sharp-angled and purple-lit, make the point. The series ran for 27 episodes before Nickelodeon cancelled it in 2002, with several finished episodes unaired for years; the audience it found on DVD, in merchandise and in the comic book that Oni Press ran from 2015, brought it back as a Netflix film, Enter the Florpus, on August 16, 2019, in which Zim's plan finally works and nearly ends the universe.

GIR is the character the show is remembered for. Every invader is issued a SIR unit, a Standard-issue Information Retrieval robot that serves as aide and spy; Zim's, assembled from junk by the Tallest as a joke, is a small silver robot with cyan eyes, a defective brain and no interest whatever in the mission, voiced by Rikki Simons in a squeal that became a ringtone. GIR wears a green dog suit as a disguise, loves tacos, pigs and a monkey on television, and has moments of red-eyed competence that never last; he is the show's chaos and its heart, and his relationship with Zim, an incompetent master and an insane servant who between them cannot conquer a suburb, is the series' whole shape.

The disguise plot is the show's version of the oldest invader story. Zim lives among the humans in a house whose lawn gnomes are turrets, attends a school whose teacher is a nihilist and whose pupils are indifferent, and is discovered by the only person who is looking, Dib, whom nobody believes because he is always looking. The Irkens are hidden in plain sight because the humans have decided not to see them, which the series plays as a joke about the audience: the planet is being invaded by a green child with a wig, and the only witness is the one everybody has agreed is a crank.

Dib is the show's ufologist, and his situation is the lore's. He has the evidence, a green alien at the next desk, and no one will look at it; his father, a celebrity scientist, is disappointed in him; his sister is bored; his only outlet is a television programme, Mysterious Mysteries of Strange Mystery, a parody of the paranormal shows of the 1990s that will air anything and believe nothing. The figure of the witness who cannot be believed runs through the real reports from Kelly in 1955, where a farm family who had shot at small silver beings were laughed out of the county, to the pilots of the 2000s, and the how to report a sighting article exists partly to explain what a Dib should do with a photograph. The hoaxes article covers the other side, the reason the audience of Mysterious Mysteries stopped believing.

The Irkens themselves belong to the empire strain of fictional aliens, the conquerors organised as a hive with a hierarchy, and their cousins are the Daleks, whose creator they resemble in their contempt, and the Zerg, who share their hive and their appetite. What Vasquez added was scale: the empire is vast and the invader is a child, the doom is impending and it never arrives, and the planet under attack has not noticed. The invasion narrative in the glossary covers the story that Invader Zim spent 27 episodes failing, on purpose, to tell.