Zim is the title character from the highly popular Nickelodeon animated series, Invader Zim (IZ). He is from Irk, a planet far out in the Milky Way galaxy. He is a short Irken defective but, despite his size, he feels that he is superior to other Irkens. A narcissistic megalomaniac by rumor and behavior, as well as speech (see "Overreaction and Overdramaticism" below), he also hates humans and Earthly culture (as would any Irken), and dreams of conquering the planet for use by the Irkens. He thinks the Almighty Tallest sent him on a "secret mission" to Earth, but the real reason was that they despise his existence, and want to get rid of him for good. Zim goes to Earth despite this, and upon arriving forms a deep rivalry with Dib, an avid cryptozoologist (or, on the show, a paranormal investigator) from the planet. He wants to conquer the Earth to prove himself great, likely more so, than for the glory of the Tallest and the empire of his homeworld, Irk.
Statistics
Zim's age is unknown, although Jhonen Vasquez himself states that Zim is older than any human being. He was created in an Irken equivalent of a test tube and has no siblings, or parents for that matter (although he claimed in "Parent Teacher Night" that he of course knew who parents were, which then led to a deep flashback to the day of his birth). His physical appearance is based on the "typical alien" design, the Greys. With his red eyes and green skin he makes a striking figure in his red shirt, black pants and black boots. He is obsessed with plotting Earth's conquest or destruction, and ordering GIR around.
Weaknesses and immunities
Zim's skin sizzles and smokes on contact with water. The episode "The Wettening" first clearly shows this, and it has since become one of Zim's primary bodily weaknesses, even in IZ fan fiction. He also hated human food (as he thought it was "human filth") until the episode "Zim Eats Waffles". Some fans suggest that Zim has developed an immunity to Earth food by this time, as throughout the episode, Zim eats delicious waffles prepared by GIR. Another fan theory is that GIR made the waffles out of Irken ingredients so that Zim would want to eat them. But it was simply because GIR added peanuts and soap.
Overreaction and overdramaticism
He has a penchant for being overdramatic, saying phrases like "I AM ZIM!" and "Silence!" (both are his trademark catch phrases), and uses ridiculously excessive and elaborate plans to conquer the planet when he obviously has the resources to do so much more efficiently. Often Zim overreacts by screaming and shouting, even just when he's speaking to GIR, his robot slave/assistant. Richard Steven Horvitz, the voice actor for Zim, later admitted on the first Invader Zim DVD's interview with the voice cast, titled "The Voices of Zim", that the constant shouting tired his voice during the recording sessions, and he would have to go home and recup "for a day, day and a half, uh, beyond that", as Horvitz himself explained. In the cancelled episode called "The Trial" (see below), it is revealed that Zim's overdramaticism and narcissistic behavior was probably caused by a corrupted data path in his Standard-Issue Irken Utility Pack, or his Pak.
Disguises for when being seen in public
Zim often wears disguises to attempt to conceal his identity from the "pig-smellies" that he has to eventually conquer. They are often poor disguises. Zim's usual disguise consists of some contact lenses and a wig resembling Pee-Wee Herman's hairdo (pictured at above right), leaving his green skin clearly visible (he falsely claims, in the first episode of the show, that it's an unnamed skin condition, most likely a form of albinoism), and in the episode Vindicated!, that his red eyes are due to pinkeye). He's been known to wear other costumes as well, like an old man disguise, an elderly woman disguise, a bear suit (actual purpose is unknown; it was most likely a running gag originating from Jhonen Vasquez's earlier comic, I Feel Sick), a poorly-constructed parent costume, and a Santa suit made from a Vortian liquid material.
Prospective occurrences during Zim's "secret mission" on Earth
If the series were to continue, Zim would have to undergo an Existence Evaluation Trial (an evaluation, based on past crimes, to determine whether an Irken is worthy of continuing to exist), get kicked out of his base by the Parent Decoys (which are robots designed by Zim to make people think he is a normal human child), and enter GIR in a SIR unit contest. After the series ended, Jhonen wrote a four-part comic for Nickelodeon magazine, in which Zim actually did conquer the earth when Dib wasn't looking, and took Dib, GIR, and Minimoose to another planet to drink space sodas and ride giant alien bunnies. This shows that if Zim ever did conquer Earth, he probably wouldn't do anything to it.
"The Trial" (cancelled episode)
In the unaired episode called "The Trial", it would have been revealed that Zim is essentially the cause of most of Irk's disasters; when he entered the information-downloading chamber, he claimed it as his own, shoving the next smeet (baby Irken) up the chute, causing a blackout that plunged Irk into darkness for five years. Later, an accident with a security robot caused another blackout, this one lasting for four years. As a military scientist, he created an energy-absorbing monster, which after ingesting an infinite energy creating device, ate Tallest Miyuki. Years later, it returned to get the collar Zim had and ate Tallest Spork. He also plunged half of the military planet Devastasis into darkness when he used a powerful robot on a malfunctioning snack machine. During Operation Impending Doom One, Zim was placed in a small circle and told to watch it, but he stole a Frontline Battlemech and destroyed half of Irk. Incredibly, he's proud of all this. Zim thought the Existence Evaluation Trial was a party to honor his "amazing greatness", but the Tallest mistakenly told him it was not. The Control Brains found him guilty as charged, and proceeded to remove Zim's Pak, which contains his soul. After the Control Brains became overloaded with Zim's narcissistic personality, the Control Brains then declared him innocent of all charges and "the most incredible Irken ever".
Voice actors
Zim is currently voiced by Richard Steven Horvitz. In the pilot episode, titled Food Fight, Zim's voice was provided first by the famous Star Wars actor Mark Hamill and then by veteran voice actor Billy West. Horvitz, however, was asked to come back, after being denied the part, to revoice Zim as a tester in the new version of the pilot, which currently is not seen on any DVD.
Personality
Zim is, as previously noted, an Irken with megalomaniacal and narcisstic tendancies, however, in Horrible Holiday Cheer, Jhonen Vasquez mentions Zim acquiring a more sensitive side by the series' abrupt end. For example, he develops some compassion for Gir, whom he reagrds as both a 'robot slave', and his only real companion. Early, he exhibits the desire to dispose of him, yet during episodes like Battle of the Planets and Halloween Spectacular of Spooky Doom, he shows concern for the robot's well-being. Character development of this nature is unusual in animated series.
Zim is extremely loyal to the Irken Empire throughout the series but his mental instability renders this loyalty unreliable.
Gaz repeatedly calls him "stupid" but Zim is quite intelligent. His recurring failures arise from overenthusiasm and overcomplication as well as GIR's constant meddling and ruining of his "ingenious" and "amazing" plans.
Zim does not qualify as an out-right villain; he sees what he is doing as the right thing. Despite his constant daydreams and occasional hallucinations, he has no real interest in ruling anything; it is conquest that appeals to him.
Zim is held in contempt by the entire Irken race, He seems oblivious of this fact except, possibly, during one small moment when he is insulted by Tak. Ironically, he and his greatest enemy, Dib, are essentially similar in that they are both outsiders— Zim is literally an alien, while Dib is isolated because his human family and acquaintances consider him to be crazy or stupid.
Fan fiction
Many fans of Zim (and Invader Zim in particular) participate in the writing of fan fiction and creation of fan-art. The most popular (albeit non-canonical) "pairings" in fan fiction are "ZAGR" (Zim And Gaz Romance), "ZADR" (Zim And Dib Romance), and "ZATR" (Zim And Tak Romance). Many of these stories take the characters out of the setting of the show to an age where a romantic relationship (xenophilia) is plausible. However this "pairing" upsets many of the fans who don't think that creator Jhonen Vasquez would ever have intended Zim to become romantically entangled with anyone, let alone Gaz or Tak, or even Dib, as he's content with just being an overconfident, narcissistic alien invader and the series never intended him to be anything but an alien with a conquest/monarchy/supremacy obsession. Some of the stories have Zim wanting Gaz or Tak to be his queen when they both rule the Earth together. This is a very heated debate within the fandom. <
Another debate in fan fiction is whether or not Zim is classified as a villain, hero, or as is most likely, an anti-hero.