After completely ruining Operation Impending Doom 1, and destroying his home planet, Irk, Zim was exiled. Almighty Tallest Red and Purple, leaders of the Irken Empire, held a meeting to discuss Operation Impending Doom 2, when Zim showed up, insisting on being reassigned. They sent him to a worthless space rock called Earth, hoping that he would never return.

Upon reaching Earth, Zim discovered that this planet was occupied by unintelligent "human stink-beasts". He set up his base, and began to work towards conquering. What is holding him back? G.I.R., his robot, which unbeknownst to Zim was made out of trash, and Dib, the only one of Zim's Skool-mates to realize what he really is.

Good characteristics in a plush toy, but not in a Standard Issue Information Retrieval Unit or SIR. Actually, these aren't characteristics in any S.I.R. They describe G.I.R. Why is G.I.R. cute and lovable instead of serious and obedient? Because it is made out of trash. What does the "G" stand for? Ummm... no one knows.(maybe garbage?)

Given to Zim by The Almighty Tallest so they wouldn't have to waste a real robot on him, (telling him that G.I.R. was a new, top-secret model) the little robot sang the "Doom Song" for over six months en- route to Earth. Zim's torture did not end there. G.I.R.'s hobbies include watching TV, especially "The Scary Monkey Show" ("~I love this show!~") and replacing its parts with food, such as tuna and cupcakes. ("~I miss you cupcake.~")

When undercover, G.I.R. is disguised as Zim's unbelievably cute, yet bizarre, green puppy and other things.

Dib is the only human who knows that Zim is an alien. After intercepting a transmission from Conventia, Dib knew that his nemesis was coming, and that it was his calling to save the earth.

Since Zim's arrival, Dib has spent all of his time attempting to expose him. Considering the quality of Zim's disguise, this seems rather simple, but the world is never on Dib's side. Pointing out Zim's green skin made his classmates ostracize him for being insensitive to Zim's "horrible skin condition." When he attempts to present evidence of Zim being an alien to the Swollen Eyeball club, the impenetrable security at his father, Professor Membrane's show prevents him from getting the mandatory permission slip signed. When he informs Zim that he will be found out for lacking organs, Zim goes on a nightmarish rampage stealing everyone's organs. Dib can't win.

Dib's father is Professor Membrane, the host of "Poking the Membrane of Science", and Gaz is his sister.

Gaz, Dib's sister, appreciates the simple things in life, like video games and pizza. But disturb her, and "you'll wish you'd never been born."

Tending to see the irony surronding her due to the stupidity of humanity, which seems to most directly come from Dib, Gaz has a scathing dry wit. She always manages to deflate Dib's bubble of his latest plans and discoveries by quietly pointing out how pointless he really is. It's unclear if Gaz believes Dib's theories on Zim, but it is very clear that she doesn't care. As long as Zim doesn't use her as an umbrella, he's as acceptable as any other kid at the Skool.

Gaz doesn't seem to have any friends or enemies, mainly because she doesn't see any reason to take time out of her gaming to interact. And she likes it that way.

In the Irken race, your status depends on your height. The Almighty Tallest are the tallest (duh) Irkens and therefore the leaders.  Since they are both the same height, they both got to rule. Their names are just Purple and Red. The Almighty Tallest are basically just jerks. They sent Zim to a faraway planet just to get rid of him.

Ms. Bitters is the teacher at the Skool. She likes to talk about implosions and doom. She seems to be half person, half snake. Her lectures, for the most part, make no sense.

Professor Membrane is the father of Dib and Gaz. He hardly has any time to see his kids, as he is the host of the hit TV show Probing the Membrane of Science. He is also a scientist.