Zim is the main character of the Nickelodeon animated series, Invader Zim. He is an incompetent alien invader from the planet Irk who is overzealous, impulsive, and convinced of his own greatness. In his attempt to regaining his leaders' trust by taking part in "Operation Impending Doom II", he is assigned to Earth and establishes a base on a mission of conquest, unaware that his leaders, the Almighty Tallest, do not expect him to succeed. Had the show continued, he would have eventually defeated his nemesis, Dib, and become a new Almighty Tallest, with Dib's sister Gaz as his consort.
Appearances in Christmas specials
Invader Zim
Zim posing as Santa in "The Most Horrible X-Mas Ever".
In the series' Christmas episode (and also the last episode produced before the series was cancelled), "The Most Horrible X-Mas Ever", Zim finds out how everyone on Earth shows great devotion to the man called Santa Claus, so he creates a giant Santa suit and uses it to disguise himself as Santa so that the humans will make him their ruler. He manages to gain the support of almost every human on Earth and commands them to build him a teleporter, which he plans to use to send the humans to be enslaved by the Almighty Tallest. However, Zim's Santa suit develops a mind of its own and starts taking over his body. Eventually, his nemesis, Dib, battles the sentient Santa suit and frees Zim from its grasp, but Zim gets back at him by dressing up as the Easter Platypus and tricks the people of Earth into thinking Dib has killed Santa.
Other Christmas productions
Zim with Jimmy Neutron in "Holiday Party".
At around the same time "The Most Horrible X-Mas" premiered, Zim also made a few cameos in the Merry Nickmas interstitial shorts. His most notable cameo in these was "Holiday Party", in which he parodies the role of the Elf Foreman from Rudolph the Red-Nosed Reindeer. When Jimmy Neutron tells him that SpongeBob SquarePants wants to be a fry cook instead of an elf, Zim responds by screaming "Who's SpongeBob?! TELL ME!!!" Zim also appeared as one of the citizens of Toonville in "How the You-Know-Who Stole You-Know-What!" In that short, Angelica Pickles tries to steal Zim's chocolate, but despite the fact that he appears to be sleeping, he keeps a very tight grip on the chocolate. Zim and his robot sidekick GIR can also be seen in the crowd of Nicktoon characters singing "The 12 Days of Nickmas".