Zim is an Irken invader who wants to conquer earth to impress his superiors: The Tallest (not aware of it being a ruse to keep him away). He's arrogant and proud even for Irken standards: thinking greatly of himself with superiority despite my plans backfiring constantly. Deep inside he's very insecure and masks his inner self with this smug, vain and narcissistic persona. Dib Membrane is his frienemy and cares deeply for him. Junk food has led Zim to obesity, much to his frustration.