Despite the fact that he doesn't realize it, he is an outcast. He was sent on a "secret mission" to destroy Earth after he ruined his superiors' plans. He constantly screws up, but is hell bent on proving himself worthy. He is desperately afraid that the humans will capture him.
Definately the most liked character, he is constantly proving that he's stupid robot with a sense of humor. Given to ZIM to aid in his destruction of Earth, he was constructed in a few seconds by the Almighty Tallest out of trash.
She's Dib's scary, gothic sister. She hates the human race, though not as much ZIM, and thinks Dib's crazy. Living her life alone, she plays her Game Slave instead of hang with friends (which she has none)
A very obsessive paranormal fan. He's been trying for years to prove any real parascience real, but so far has failed. Many of the kids at SKOOL think he's crazy, and he now tries desperately to prove that ZIM's an alien. Unfortunately for him, because everyone thinks he's crazy, no one believes him.
One of the teachers at SKOOL. She teaches Zim and Dib, She's very old and very scary!
Allmighty tallest Red and Purple
Zim, and all other Irken Invader's, leaders. They are both the same hight, so they must share the duty of leading the Irken Empire. They assign all the Invaders there jobs.
Father of Dib and Gaz. He is a great and famous scientist, and thinks Dib should study real science. He spends very very little time with his kids, once a year they have a familiy dinner.
A kid Zim, regretibly, made friends with so people would beleive he is human. Eventually he threatened Zims mission, so Zim tricks him into thinking A squirl is really him. Eventually Keef was suposed to return in a later, cancelled, episode.