Zim is an alien from the planet Irk who is trying to take over Earth. He goes to Skool with Dib in Ms. Bitters class. Zim cannot be touched my water and he doesn't eat food. The other students juts call him "the green kid." Dib is the only one who can figure out that Zim is not from this planet. Zim tries everything he can to destroy Dib, but his plans always seem to backfire.

GIR is Zim's somewhat faithful, but completely clueless robot. GIR was made from garbage, so as not to waste a real robot on Zim. He loves to eat anything from tacos to candy. GIR is supposed to help Zim, but he often fails his tasks. His disguise is a green doggy suit. GIR loves TV and his favorite show is the Scary Monkey Show.

Dib is Zim's one true enemy. He is always trying to break into Zim's house. Dib loves studying paranormal stuff like bigfoot and aliens. He knows Zim is an alien, but he can never prove it to anyone. Dib's favorite TV show is Mysterious Mysteries. He is in Skool with Zim in Ms. Bitters class. Professor Membrane is his father.

Gaz is Dib's sister. She loves pizza and video games. The one thing that she despises is Dib. She would be content if Zim did in fact destroy him, because Dib always seems to come between her and the things she likes. She goes to Skool but is in a different class. Her dad is Professor Membrane.

Ms. Bitters is Dib and Zim's creepy teacher. She is a very bitter old woman who hates children. She is always having to punnish Dib for being late. Ms. Bitters moves like a snake, and she can float in the air too. She teaches some odd subjects.

Professor Membrane is Dib and Gaz's dad. He has his own TV show about science. It's one of the most popular TV shows around. He also has a lab in their house where he can do his experiments and research. Dib is always trying to get access to his father's lab.