As a result of the incredibly large "Happiness probe" screwed into his head, Nick is freakishly happy about everything, even when horrible things are happening; in "Zim Eats Waffles", while Zim is being attacked by cyborg zombies, Nick declared the mindless pleasure he was feeling.
In Nick's first appearance, he was shown inside a tube with various other tubes inserted in his neck and head. In all subsequent episodes, he has appeared with his trademark head probe.
His shirt bears the old Nickelodeon logo shaped like an orange splat. Given his excessively happy nature, it's likely that the character was created as an act of ridicule against the studio, as they did not permit Jhonen to incorporate some of his intended ideas into most of the episodes (such as blood, or characters getting killed) and forced him to change them to make the episodes more tame. Nickelodeon didn't even seem to realise that Nick was based on them, even though it was rather blatant. Through the character Nick, he was apparently subliminally stating that the studio wants every show to be sweet, happy and saccharine, no matter how horrible the events corresponding actually are.
Nick is voiced by Jhonen Vasquez himself, who has also voiced numerous other minor characters.