No one realizes that Zim is an alien, except Dib and Gaz. Zim has no friends, and often physically harms his classmates if they attempt to befriend him. However, despite this, they always naively defend him when Dib tries to warn them that Zim is a space alien. Zim is equipped with a PAK, a cybernetic backpack-like device with life support and (among other gadgets) long, retractable robotic spider legs that enable him to move about quickly and climb almost any obstacle.