Disguises are a vital tool required by Irken Invaders so that their true identities are not exposed to the inhabitants of the planet they are assigned to conquer.
They are each given a special piece of cutting-edge technology from which they can choose a disguise based on what the inhabitants of their assigned planet consider "normal". However, almost all Irkens choose awful disguises, despite having a handful of excellent options to choose from.
Like their Irken masters, SIR Units also require disguises; most creatures would become suspicious if they caught sight of Irken technology on their planet, since most beings in the Invader Zim universe are, consequently, aware of the Irken race's mission of galactic conquest.
- Main article: Zim's Disguises
Zim first disguised himself as a human boy, and attended Skool, where he hoped to learn about Earth's weaknesses. Zim's human child disguise consists of two contact lenses to make his eyes appear human, and a black wig to cover his antennae. He manages to pass himself off as a human by claiming to have a skin condition.
He also has other disguises seen through the course of the series, such as an old man disguise, a Santa suit, an Easter Platypus costume, a fat woman suit, a bear suit, a "Baby Inspector" uniform, a rarely-used "Human" suit, a "Professor" diguised used in Enter the Florpus and an unseen clown disguise that he used only once in "Nubs of Doom".
GIR's main disguise is a light green dog suit, with a vertical stitch stretching down the face, a square red tongue, an oversized zipper, and black paws. The suit can also be put and taken off like a hoodie. However, he acts nothing like a dog, walking on two legs and even speaking in front of humans.
However, because almost all humans are oblivious to these hints, they do not notice that GIR is not a real dog. On the contrary, his disguise, and its inherent cuteness, seems to gain the positive attention of teenage girls, as seen in "Attack of the Saucer Morons".
Human Boy Disguise
GIR also has a little brother disguise, which was only used in "Door to Door" and "The Most Horrible X-Mas Ever". It is poorly made, the head being noticeably large with several patches and stiches. Unlike GIR's dog suit, it shows GIR's real eyes, which are seen through the suit's mouth.
Another human boy disguise can be seen in Issue 26 of the comic series. GIR goes to skool and poses as one of the students. He is able to make friends with the skoolchildren and gather secrets from them. Zim thinks he can use this information to take over the planet, but it turns out to be useless trivial skookchildren matters. He goes by "GIRB" in this disguise.
During "The Most Horrible X-Mas Ever", GIR donned an elf suit for a few moments, wearing a green Santa hat, elf ears, a vertically striped suit and a vest over his regular dog suit.
In Issue 38, GIR is crushed by a piece of machinery in public while wearing his dog disguise, causing all the watching skoolchildren to think he's died, rendering the dog costume useless. Zim then tries to make GIR a new replacement disguise but quickly gives up, telling GIR to make one himself. For some reason, GIR settles on a disguise that looks like Dib.
Despite it being just as poor as his other human disguises, the skoolchildren can't tell GIR and the real Dib apart, and eventually come to the conclusion that Dib is a clone and chase him into the woods. GIR then impersonates Dib for a while, until he gets too into the role and tries to expose Zim as an alien, ultimately resulting in Zim destroying the Dib disguise in the process of defending himself.
Invader Flobee's Disguise
Incredibly his SIR Unit didn't wear a disguise, another clue that the inhabitants of the planets are not intelligent.
Invader Slacks' Disguise
Something of an anomaly among her Invader peers, Tak takes a different path when it comes to disguise; rather than a physical disguise, she used a hologram that is presumably projected from an implant in her right temple.
It is almost completely perfect; the only problem is that it does not mask that she only has three fingers. Her disguise somewhat resembles Nny from JTHM .
Tak's SIR Unit, MiMi, is disguised as a black cat with red eyes. The ears are gray and striped. She is also disguised using a hologram.
There are many other Invaders whose disguises have not been seen.
Invader Skoodge, assigned to the planet Blorch, home of the Slaughtering Rat People, may have not have needed a disguise, as the rat people are probably not sapient, though they are extremely vicious creatures and if he did used a disguise its probable that it was paper thin as the other Invaders. Surprisingly, Skoodge not only conquered these hideous creatures, but was the first Invader to successfully conquer a planet during Operation Impending Doom II.
Invader Larb was assigned to the planet Vort, home of the Universe's Most Comfortable Couch. The Vortians are an extremely intelligent race of alien scientists, who created the Massive, and were once allies of the Irken Empire, until Zim created an energy absorbing blob that devoured Tallest Miyuki and later Tallest Spork on Vort Research Station 9. Because of the Vortians' intelligence, Larb and his SIR Unit would have needed a brilliant disguise like Tak's, or they would have seen through him.