The voice of GIR is provided by Jhonen's friend, Rosearik Rikki Simons. Simons does the coloring for Jhonen's color comic books and the coloring design for "Invader ZIM".
Jhonen's infamous "Z?" logo appears frequently in the show, as well as Fillerbunny, one of Jhonen's comic characters.
Four completed, unaired episodes were left hanging in the balance when Nickelodeon canceled the show. Those episodes are titled "Backseat Drivers from Beyond the Stars" (#2.1), "Mortos Der Soulstealer/ZIM Eats Waffles" (#2.2), "The Frycook What Came From All That Space" (#2.3), and "Vindicated!/The Voting of the Doomed" (#2.4). All four were included on Volume 3 of the Invader ZIM DVD release.
In the episode "A Plague of Babies", the goth vampire from series creator Jhonen Vasquez's "Meanwhile..." comic is visible in the background of the first baby's house.
Bloody GIR is an Easter Egg visible in several episodes of the series. To see him, one would likely need a DVD player capable of viewing screens frame by frame. The most visible instance of bloody GIR is in the opening sequence of Mortos der Soulstealer. The image is evident for at least two frames in the end of one of the pipes that snakes out of Zim's house. Bloody GIR has also been sighted in Bad, Bad Rubber Piggy as the last pig goes through the "space time object replacement device". He has also been seen in the voot cruiser sequence in the opening of Plague of Babies. He is seen looking in the window of the voot at the left hand corner of the screen several times, some more noticeable than others. Bloody GIR was born when Jhonen drew an image of GIR covered in blood. He wanted to make an episode that featured bloody GIR but Nickelodean would not allow it. He decided to slip the image into several episodes without their knowledge.
The producer, Steve Ressel, appears in some episodes, in cartoon form. He is the fat man with long black hair and glasses.
The creator, Jhonen Vasquez, appears in some of the episodes, in cartoon form. He is the tall man with orange spiky hair and glasses.
In the episode "The Nightmare Begins", when Zim is picking a disguise to use on Earth he claims one is "too ugly" and another "too stinky". Those disguises are pictures of Jhonen Vasquez and Steve Ressel respectively; two of the creators of the show.
The original name for Zim's ship was to be the "Spoot Cruiser" but the phrase spoot had already been made big in The Angry Beavers, so they made it the "Voot Cruiser" instead.
The vampire featured in the game Gaz is playing on GS2 is D from the Vampire Hunter D movies.
Before Richard Steven Horvitz got the job, Mark Hamill and Billy West were hired to voice ZIM. At the time, Horvitz was doing the voice for Dagget on The Angry Beavers, and Nickelodeon didn't want the same actor on two current shows. Hamill originally voiced ZIM for the pilot episode. When Hamill was dropped, his parts were dubbed over with West's voice. The creators decided that both Hamill and West were too well-known, and finally hired Horvitz when the The Angry Beavers series ended.
Frequently, after GIR drinks something, he launches into an inexplicable coughing fit. What you hear are actual recorded real-life coughing fits of GIR's voice actor, the asthmatic 'Rikki Simons', who could not perform GIR's enthusiastic slurpy drinking noises without aggravating his breathing.
Jhonen Vasquez asked the animators to stop putting cameos in the series after about episode 10. He felt that the cameos drew attention away from the show and that people would only watch for the cameos. Vasquez's creations (comic characters, Z?, references to his other works, etc.) still continue to appear, but no more Jhonen.
If the show had not ended, the following events and stories would have taken place: - Invader Skoodge would have moved in with Zim on earth - Dib would have discovered he is a clone of Professor Membrane and not actually his son. - Tak would have returned. - Zim and Dib would have left Earth and had a season where Dib chased Zim across the galaxy on their way to Irk. - The Resisty would have returned - And a series finale movie entitled "Invader Dib" would have had a full scale war against the Irkens.
The show's main characters all have names that are three letters long (Zim, Gir, Dib and Gaz).
Although Zim is the show's title character, the most frequent title character of the episodes themselves is Dib - four episode titles contain his name in one form or another: "Battle-Dib", "Future Dib", "Dib's Wonderful Life of Doom", and "Dibship rising." Zim's name appears in only two titles ("Nanozim" and "Zim Eats Waffles"), while GIR, Gaz, Tak, and Mortos have one title each.
One of the many running gags in the show is the unnaturally frequent use of the word "Doom" and its derivatives. It's the most common word in the episodes' titles (not counting the "The", of course), and is also spoken by at least one character in most of the episodes themselves, especially in the first episode where it's uttered about 100 times by four different characters.
Most of the show's characters appear to be crazy in one way or another. In particular, Zim has delusions of grandeur, GIR is completely insane, Dib is obsessive and often talks to himself, and Gaz is rageaholic with multiple addictions. Throughout the series, the words "crazy" and "insane" are repeatedly used to describe all of the main characters.
Among the items visible when Gaz opens the refrigerator, is a jar labeled "Liquid Pig Toes", and a milk carton. One one side of the carton it says "MILK - best before juice", and on the other - a picture of a guy signed "ROB HUMMEL is MEAT". Rob Hummel is the show's writer. However, moments later when the insides of the refrigerator are shown again, the picture is completely different and the writing on it says "Find me! I've been stolen."
The word "doom" along with its derivatives is uttered approximately 100 times throughout the episode, mostly by GIR during his "Doom Song" and Ms. Bitters during her "The Universe is doomed" lecture.
SPOILER: According to Jhonen Vasquez, Dib was meant to be killed off in the end of Bad, Bad Rubber Piggy and be replaced by a new child adversary for the remainder of the series. However Nickelodeon was uncomfortable about killing off a main character and refused this idea.
The start of the episode was originally supposed to start with Zim and GIR buying snacks before flying into a billboard. This scene was cut for time constraints.
A framed picture of the vampire from Johnny the Homicidal Maniac is seen on the wall when Zim enters the woman's house disguised as a baby inspector.
Originally Tommy Pickles (from the Nickelodeon show, Rugrats) was supposed to be one of the alien babies, however Nick execs rejected this idea.
The Swollen Eyeball Network's phone number Dib gives Gaz is 1-555-555-0199.
On the episode "FBI Warning of Doom", GIR starts over his movie around the time Zim enters and sees the FBI Warning which appears on most movies at the beginning. "WARNING OF DOOM! Federal law provides severe civil and criminal priorities for the Unauthorized reproduction, distribution, exhibition of copyrighted motion pictures in any medium (Title 17, United states code, Section 201 and 506.) This Federal Bureau of investigation investigates allegations of criminal copyright infringement. They will hunt you down like the dirty monkey you are and force you to wear a moose skin and ride a greased piggy while singing folk tunes. They're forcing me to ride the piggy as I write this. The Piggy is Smelly!!"
The Virtual Reality scene originally contained New York City in flames during the Zim's sales pitch. Due to the 9/11 attacks, the episode was pulled from it's original airdate so a new scene could be animated in it's place. However due to a mishap, when the episode first premiered, it had the New York sequence instead of the new scene.
Poop Dawg was originally going to be Poopsy the Clown.
The Grout children were originally supposed to be eating cockroaches instead of cocktail weenies.
The credits listed in the movie "Intestines of War" are: - The General (Ress Stevel) - Sarge (Steve Ressel) - Private Poop (Himself) - Nurse (J. Duffi) - Private Hack (Kriz Graf) - Colonel Colon (Ion) - The President (Hed Cheez) - Captain Dook (Gurge)