Invader Zim is the titular protagonist and anti-hero of the series by the same name.
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 Irk during Operation Impending Doom I) 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 School to begin his infiltration and gather information about the human race. There, he became quick rivals with Dib, an avid preteen paranormal investigator.
Zim's primary desire is to conquer Earth, mostly to prove his superiority and impress his leaders. However, as mentioned by Gaz in Bloaty's Pizza Hog, "He's so bad at it."
Although he is the protagonist, Zim is morally, and ethically a villain, being overall a fairly unsympathetic character, though he occasionally shows some kindness towards certain characters, (such as GIR in Walk of Doom), and is usually only causing chaos and destruction for either himself, his own race, or Earth. As well, almost everyone else he comes into contact with at any time. His unawareness of his destructive actions is most likely the result of him being a "defect", as revealed in the cancelled episode The Trial.
Zim's appearance, like that of most of the Irken race, seems to be based off the typical "little green men from outer space" stereotype. Many Irkens are about the size of a preteen schoolchild, but Zim is exceptionally short. In The Nightmare Begins, Zim was shown to be even shorter than the notoriously diminutive Invader Skoodge.
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. Since the eyes he was born with are not visibly different from subsequent appearances, it can be assumed that these implants are subcutaneous. As he considers himself to still be an Invader, he continues to wear the standard uniform: a red tunic-like garment with a pink collar and sleeves, as well as black boots and gloves.
He also possesses a pair of antennae; their exact function is unknown, but they seem to function like human eyebrows; rising and lowering to convey emotion. It is possible that they also function as an organ in place of ears, as they picked up vibrations in Battle of the Planets.
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 rare:
Despite his self-proclaimed greatness, Zim rarely succeeds in his attempts, and is held up as a complete laughingstock by his own people - a fact that he is either oblivious to or simply chooses not to notice. Zim is cluelessly 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. However, his self-absorbed nature prevents him from acknowledging any of his failures, and he chooses only to speak about the better things that came from each incident.
Zim's laugh and mannerisms can be said to be somewhat derived from a masculine equivalent to the unpleasant "ojou" stereotypes common in anime and manga, and "rich person"/"popular schoolgirl"/"spoiled brat" stereotypes of Western animated cartoons and movies, combined with the "overconfident alien invader" stereotype seen in sci-fi shows and movies.
Despite his frequent displays of stupidity, it is clear that Zim is highly intelligent in some respects - being a keen manipulator of tools and devices - but has absolutely no apparent interest in thinking things through, and wastes much of his time fretting about or dealing with unimportant "threats." Moreover, it is evident that he is more than capable of conquering the Earth, yet he hardly ever uses this capability properly, and has often been very close to taking over the planet, only to be thwarted by his own negligence.
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.
Even though Zim often affirms that he wishes to enslave Earth, it has been hinted that he would not actually want to rule it. In Attack of the Saucer Morons, Zim gained a group of human worshipers who would be willing to do his bidding, yet his only thought was escaping them. In the non-canon Nickelodeon Magazine Special, in which Zim finally took over the world, he did not stay to rule for very long, instead leaving Earth forever to ride flying alien rabbits and drink soda.
Zim usually shows little to no affection, often claiming to "need no one", but he occasionally lets a softer side of him slip by accident. In Parent Teacher Night, when Zim thought back to when he was born, he remembered the first thing he ever said was that he loved the "cold, unfeeling robot arm" that "hatched" him from his incubation capsule and activated his PAK.
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. 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.
- Zim could've been considered the first Nicktoon villain to have ever killed anyone onscreen had the show not been cancelled, since the unfinished episode The Trial confirms that he doomed two previous Irken leaders by accident; and, during a flashback in The Frycook What Came from All That Space, it was shown that he blew up all the other Invaders at the beginning of Operation Impending Doom I.
- Zim may have appeared in Jhonen Vasquez's comic book Squee! before the start of the series. A poster featuring an alien that looks Irken and wearing a wig like Zim's bouffant wig appears above Todd's bed. The image looks less like Zim, though, since the head is rounded and has mere stick figure hands.
- Zim has been seen in a commercial on Nickelodeon holding a sandwich, to which he has bad allergic reactions. In it, he was knocked off a wire he was sitting on and thrown into a light, making it explode. This commercial was a crossover of other series on Nickelodeon. After the cancellation of Invader Zim, Zim was replaced with Jenny from My Life as a Teenage Robot, which was also cancelled. However, Jenny wasn't knocked into the light.
- Zim is known to smell things and scents even though he does not have a 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."
- In Jhonen Vasquez's Meanwhile... comic "Jhonen Vasquez V.S The Devil," there are aliens flying a ship similar to Zim's Voot Cruiser, though the aliens inside the ship look nothing like Irkens.
- Its revealed in Tak: The Hideous New Girl that he promised the moon to GIR.
In one episode of FanBoy and Chum Chum called "Dollar Day," Invader Zim can be seen on a comic cover in the background. His skin is faintly green and he is wearing his disguise, so one must be careful when looking for him.
- At some point in the series, Zim had learned to read human writing, as he is seen reading the newspaper, and understand what it says, in Zim Eats Waffles.
- Zim's weaknesses have little consistency within the show. For example, in The Wettening, it is made obvious that he gets burned by water, but in many other episodes, he comes into contact with water and is just fine.
- Zim is a playable character in Nicktoons: MLB, alongside Gaz; best used as a first base-Irken, his bat is one of the strongest in the entire game if Turbo Hit is activated and he maintains his concentration. His clothes and overall body rendering are the same as in the show, only he wears a pinkish baseball cap that transforms into a first baseman's helmet when he is in first base. He also has a collectible card that mentions that he was almost cut from the roster when it was discovered that he was pulling a prank on fellow team players (tying their shoelaces together). His 'up to bat' pose is an action movie-style jump. Gaz cheers him on when he gets a home run, as do the hundreds of Irkens in the stands when he knocks the ball out of the park.
- Zim's name is spelled in capital letters in the official voice scripts.
- Other media forms stylize his names in the same fashion, and some people consider it the canonical way of writing his name.
- Jhonen Vasquez stated that Irkens write in all caps "because they are annoying"
- Zim makes an appearance in two of Snafu's webcomics: PowerPuff Girls Doujinshi, and Invader Zim: Manifest Doom.
- In the Japanese and Latin American dubs of the show, Zim is voiced by a woman. In the latter, his Spanish voice actress's voice is pitched down to sound more male in initial episodes.
- In Japanese, Zim's name would actually translate into Jim, as Zim would be difficult to translate.
- The unfinished episode "The Trial" implies that Zim may have an actual disorder, as the titular trial amounts to a process of Zim being declared legally insane or suffering from paranoia and mania.
- In The Nighmare Begins, Zim draws his base on a tablet first. If you watch closely, this shows that Zim draws it with his left hand. Yet in Career Day while taking the ink-blot test, he writes with his right hand. So Zim is ambidextrous.