Zim

Gir - green dog-like creature with a big zipper on his chest. GIR is apparently Zim's only true friend, although in reality he is his faulty servant robot. The two of them get along, GIR is like his insane and hilarious younger brother, or perhaps his disobedient young son

Dib - schoolboy and Zim's classmate. Dib is Zim's mortal enemy during his "mission" on Earth. It's quite evident that the two hate each other, but because Dib is the only one (aside from Gaz) to know he's an Irken Invader, Dib has made it his mission to expose Zim for the "evil menace he is"

Zim goes to ordinary school and pretends to be an ordinary schoolboy. often he talks very expressively like this: "I ABSOLUTELY will DESTROY your FILTHY stupid little PLANET!!!"

As revealed in Zim's flashback to his birth in the smeetery in "Parent Teacher Night", Zim's first words were "I love you". These are words that he has never spoken to anyone else afterwards, not even to Almighty Tallest Red and Almighty Tallest Purple (the Irken leaders whom he worships and idolizes), and not ever to GIR, Gaz or anyone else.

Zim is known to smell things and scents even though he does not have a visible nose, or his nostrils are so small that they're not visible, as evidenced in "Germs", when he is seen sniffing the scent saying it was the "stink of clean".

Despite Zim being widely hated within the universe of the show, he is also quite respected by some.

Ironically, Zim is the closest thing Dib has to a friend.

In some rare cases, Zim has a habit of procrastinating on his mission.

Zim would have been the only known Irken defective to not be deactivated seeing as the Control Brains themselves would have become insane from all the bad data in his PAK.
Interestingly, the Control Brains can re-encode Zim's PAK from an Irken Invader to a Fast Food Drone without any problems but as mentioned above are unable to erase his PAK.

Ironically despite Zim wanting to enslave or destroy the human race, he seems to have a decent amount of "popularity" among not just the Skoolchildren but with a few citizens as people often side with him rather than Dib even when it is painfully clear that he hates humanity at the moment, at least for the majority of episodes that were completed before cancellation.

Interestingly since Zim accidentally discovered Earth, other aliens may be aware of his discovery.

Zim has only cried twice during the duration in the series.

Zim's school disguise consists of some contact lenses and a bouffant wig. The contacts give his eyes a human appearance, and the wig covers his antennae; however, everything else about him, including his uniform and green skin, is left unchanged.

Zim, like all Irkens, was fused at birth with a mechanical device called a PAK. Zim's PAK provides him with life support, all the necessary nutrients for survival, and an array of different weapons and tools.

These tools include a set of four spider-like mechanical legs, an organ harvester, scanner pads, hand-held communicators, memory drive, charging cell, atmospheric processor, high tech infrared/night vision binoculars, holographic transmitters, and four rocket boosters, as well as a sort of biomechanical rebreather mask used in environments without air or with polluted air. It can also be 'rebooted' and revive Zim after a sudden shock to the system.

an Irken PAK contains all of a single Irken's memories, personality, and high scores. An Irken assigned to a specific task has their PAK 'encoded' for that task by an Irken Control Brain, similar to formatting a hard drive. Zim is defective and his PAK is broken

Unfortunately, this depression however didn’t last for long as it was shown that after Zim truly has the potential to be an actual threat if he puts his mind to it. He successfully hijacked Professor Membrane's Peace Day ceremony, but only after Dib unintentionally inspired him (and he even rubs it in his face about it), it could be said that his determination to get back on the Tallest's good side was the driving force behind his successful teleportation of Earth, making it clear that there is nothing Zim wouldn’t do to earn the approval of his leaders and his people.
Earth was moments away from being destroyed and taking humanity with it, Zim showing a complete indifference towards his own life because his mission, even if it was his last one, would've been complete.

Zim sounding so triumphant while stepping into his own doom is quite fanatical because his loyalty to the Irken Empire knows no bounds and he is no doubt willing to go out like a soldier doing his duty.

If he removes his PAK, with the exception of the life support and personality components, perhaps all the aforementioned negative traits of his personality can change, such as the aforementioned minimal showing of affection or care for others.

Strangely, it would seem that Zim also relies on the presence of his mortal enemy, Dib, for motivation. He said in "A Room with a Moose" that his mission might not be as "exciting" without Dib around to "annoy him", but also seems to dwell on the big-headed human quite a bit, sometimes more so than his actual mission.

In fact, Zim enjoys tormenting and humiliating Dib even if it is unprovoked that he would just do it for the fun of it, making Dib's hatred for him real and his efforts to beat the Invader all the more personal. This importance was particularly highlighted in "Mopiness of Doom": When Dib briefly decided to give up his pursuit of Zim, the Irken lost all motivation to take over Earth or do anything in general.
it was shown that Zim is not as delusional towards the relationship he had with his leaders as it was shown that could see the truth (even if temporarily) since he could no longer be in denial after seeing the Massive’s flight plan and seeing that Earth was “Smillions of light years away from the Irken Armada, this turned him go into a mopping mess once he realized that he doesn’t have the respect of his leaders was just about ready to give up on his mission and allow Dib to expose him to the rest of the human race.

Even though Zim often affirms that he wishes to conquer Earth, it has been hinted that he would not actually want to rule the planet himself, like aliens in other sci-fi shows and movies would (perhaps ruling his home planet Irk instead). It has also been suggested that he prefers simply to do his job as an Invader rather than becoming master of the inhabitants he wants to conquer or destroy.

Zim shows no remorse for the people that are harmed due to his actions and almost never takes responsibility for his mistakes, priding himself on causing destruction in the name of the Irken Empire, even when said destruction is aimed towards other Irkens. However, he has been shown of being capable of forming temporary alliances with others, such as Gaz in both Issue 16 of the comics and in the cancelled episode "Ten Minutes to Doom". In the former, by agreeing to take Gaz to Arcadikon, it is shown that he understands her wants and values her interests, showing a level of understanding with her. In both of these instances, he also does not wish to have her come to harm in any way, shape or form, also suggesting that he may deep down value her in some form.
More or less he considers everyone else but himself (even members of his own race) expendable for his own plans, often exploiting them to reach his own goals with apparent disregard for their safety or well-being.
At the moment, Zim is most comfortable in ensuring destruction rather than gaining power and when he does gain power, he seems not to care much for it, treating it more like a means to an end since it has been heavily implied that he only seeks to take control of the planet to mainly earn the praise and respect of his leaders.

At the moment, Zim usually shows little to no affection publicly, once claiming to "need no one", but he occasionally lets a softer side of him slip by accident.

Unsurprisingly this has been previously shown to be the case as in "Bad, Bad Rubber Piggy", Zim used a Temporal Object Displacement Device in order to torture Dib with rubber piggies with the ultimate goal of eliminating him over an extended period of time, the fact that Zim decided to kill Dib over several years rather a quick demise implies a sadistic side as it was seen that Zim enjoyed the outcome each time.

Curiously when Zim briefly believed he succeeded, he didn't laugh manically or claim a loud victory like one would expect from him but instead celebrated with a drink and dismissively called Dib a "Foolish Earth creature", this could be because in Zim's eyes, Dib is nothing more than an annoyance that keeps him from completing his mission and as a result Zim may have viewed the human's temporary death as an insignificant thing rather than the passing of a worthy opponent.

Despite his many failures since his mission began, it shouldn't be overlooked that Zim has often come very close to taking over the planet, only to be thwarted by Dib or Gaz, or even his own negligence, Jhonen Vasquez has gone on record by saying that Zim has a "horrible sense of direction" and he is so preoccupied with unimportant "threats" that he doesn't get anything done, this may be a result of his paranoia.

One of Zim's abilities is his somewhat inconsistent skills at piloting; while in a tense situation he flies masterfully but seems to crash on most other occasions, and his skills pale in comparison to opponents adept at hand-eye coordination or overall agility (such as Gaz). Zim also has admirable engineering ability; in "Walk of Doom" he singlehandedly improved the SIR Unit guidance system chip, and in "Walk for Your Lives" he hand-built a variable time stasis field capable of altering individual time-fields. He is immensely proud of anything he creates, yet is often frustrated when his devices fail to live up to his grandiose expectations.

Zim's laugh and mannerisms are overly theatrical, which is fitting for his dramatic personality. As seen in "Future Dib" and "Bolognius Maximus", he can let his maniacal laugh linger for too long and be unaware of the disturbance he causes.

By turns this would-be Invader can be petulant, critical, paranoid, humorous, sarcastic, pretentious, pedantic, depressive, melodramatic, and even occasionally whimsical. He is often curiously attached to random objects, such as his robot bee ("Tak: The Hideous New Girl") or Li'l Meat Man. He is immensely proud of anything he creates, yet is often frustrated when his devices fail to live up to his grandiose expectations.

It's clear that Zim is highly intelligent (in his own crafty sort of way) and is a keen manipulator of tools and devices, but has absolutely no apparent interest in thinking things through to their logical conclusion. The fact that creating and unleashing a giant water balloon on the city from orbit in "The Wettening" will also destroy his house (but not his base) doesn't seem to enter his mind.

When he hijacks the Massive in "Backseat Drivers from Beyond the Stars" he only considers (incorrectly) that the Tallest will be appreciative of his efforts. Nor does he really consider the consequence of restoring the natural time-flow of a city-leveling explosion in "Walk For Your Lives", despite being warned several times, by GIR no less, until his base was coming down around him. An alternative explanation is that he is aware of the consequences of his actions, but believes that they are worth reaching his goals and is willing to amend them after he does so.

When he is told by Tak in "Tak: The Hideous New Girl" that his "mission" was really an attempt to get rid of him, he simply rejects her statement as a lie. It is not entirely clear whether Zim is aware of his failings in the eyes of his leaders and is desperately trying to compensate for them, or whether he really is just completely oblivious to the opinions of others, as he had deluded himself into thinking he's "amazing" and can do no wrong.

Despite this, Zim is innocently loyal and obedient to the Tallest, the Irken Empire, his planet and his people, and is willing to go to ridiculous lengths to please his leaders, to the point that he is zealously willing to endure pain or hardship in order to gain their respect. In the episode "Planet Jackers", Zim even undergoes a rather severe beating in the name of protecting his mission and for the sake of Irken benefit.

Interestingly despite the fact that Zim has both a strong hatred for humanity (at the moment) and is a well known defective he refuses to abandon his post on Earth as seen in “The Frycook What Came from All That Space” where his main concern was to escape the restaurant in which he was being held captive by Sizz-Lorr so he could return to his “secret mission”, this is most likely because he’s under the belief that he’s still an Invader and had a mission to fulfill while he only saw his initial exile on Foodcourtia first as “vacation” that he claimed didn’t need and later as a horrible experience that kept him away from conquering his "assigned planet” and after he escaped a second time, Zim happily returned to Earth, eager to continue his mission and was even relieved to be “home”.

While most Irkens are expected to be ruthlessly loyal to the Empire, Zim is considered overzealous even by their standards: Brash, arrogant, and overconfident, Zim's tendency to cause wanton destruction makes him a danger to himself and his own people, yet he still considers himself a mighty Irken warrior. In addition, he is acutely narcissistic and megalomaniacal, congratulating himself on even the smallest of successes; these, however, are few and far between. However, the pride he feels for his planet and its culture, as well as its people, is to be admired and respected by all.

Zim's loud, petulant, overbearing and harsh personality (under the influence of his PAK of course) was envisioned by Jhonen Vasquez as a direct parody of the hyper-intellectual, highly arrogant alien overlords found in 1950s and 60s B-movies and television series.

Despite his self-proclaimed greatness, Zim rarely succeeds in his attempts and is sadly held up as a complete laughingstock, a scapegoat, or a figure of contempt by his own species, a fact that he is either oblivious to, knows about but keeps a brave face, or simply chooses not to notice; this is hinted at by the fact that due to his self-absorbed nature (and the influence of his PAK), it prevents Zim from seeing his failures, past and present. He claims to be proud of all the past disasters he has caused (as revealed in "The Nightmare Begins" and in the unproduced episode "The Trial", and rarely acknowledges his defeats in his present mission on Earth (often blaming them on other characters like other supervillains do, or other factors, or completely changing the subject).

Zim, like most of the Irken race, seems to be based on the typical "little green men from outer space" stereotype. Many Irkens are about the size of a preteen schoolchild, but Zim is at the moment exceptionally short, earning him ridicule from his fellow Irkens, who are respected only if they are tall in height rather than be respected by character, inner worth or skill, as confirmed by Dib in the episode "Tak: The Hideous New Girl". This could be an equivalent to social stratification (i.e. based on wealth or birth status or on derived power, either social and political) found on other planets or dimensions.

In "The Nightmare Begins", Zim was shown to be even shorter than the notoriously diminutive Skoodge. In addition to his short stature and green skin, he also has round teeth (resembling gums more than actual teeth), and a long, worm-like tongue.

Zim also has ruby-colored eyes; a very common trait in Irkens. It was also mentioned in "Walk of Doom" that Zim's eyes contain ocular implants.

As he considers himself to still be an Invader, he continues to wear the standard uniform: a red tunic-like garment with three black stripes and a triangular pink collar and sleeves, as well as black boots, leggings, and gloves. His PAK is light gray with pink spots.

He also possesses a pair of antennae, however, their exact function is unclear. His antennae visibly pick up vibrations in "Battle of the Planets". In Enter the Florpus, Zim's antennae convey emotion by either standing alert or drooping while he "schmoops".

Zim is a member of the alien Irken race and a former Irken Invader. However, since his actions usually lead to disaster (having nearly destroyed the Irken homeworld during Operation Impending Doom) his leaders, the Almighty Tallest, banished him to Foodcourtia. While there, however, Zim heard of Operation Impending Doom II, and - obviously not understanding the purpose of his previous exile - "quit being banished" and ventured to Conventia in the hope of getting an assignment. Chagrined, the Almighty Tallest sent him on a "secret mission" to Earth, in order to keep him occupied and away from the real Operation Impending Doom II.

After arriving on Earth, Zim enrolled in the nearest elementary skool to begin his infiltration and gather information about the indigenous races. While he could have enrolled into any of the Skool's classes, he ended up in Ms. Bitters' class. There, he became quick rivals with Dib Membrane. Zim's primary desire is to conquer Earth, mostly to prove his superiority and impress his leaders (who despise him).

The debate about him being a sympathetic villain is ambiguous because he is seen as evil due his "job" as an Invader, but has been mistreated and ridiculed by his species for almost his entire life, though he is oblivious to their hatred and considers his actions "good for the Empire", despite evidence to the contrary such as obliviously almost annihilating the entirety of Irken civilization (albeit by accident).

He usually only causes chaos and destruction for either himself, his own race, or Earth. Despite all this, he occasionally shows some kindness towards certain characters (such as Gir)

The viewer knows that Zim is an alien, but on the Invader Zim version of Earth most humans are oblivious or unknowing to this with the exception of Dib and Gaz, as well as a few others, who are the only ones that know that he is not from this world.