The series follows Zim,the Irken invader,Gir the robot sidekick,Dib the Earth`s hero and Gaz the cool gamer girl.
Zim was banished to Foodcourtia as punishment for destroying Irk but quit when he found out about Operation Impending Doom II.
The Almighty Tallest issued Gir to Zim as a "top-secret model".
Gir is usually disguised as a dog but strangely nobody thinks it`s weird that the dog is green.
Dib notices that Zim is an alien from the start because he`s green and doesn`t have ears.
Gaz is aware that Zim is an alien but she doesn`t care.