In the first film he is voiced by Jeff Daniels, while in the sequel he is voiced by John DiMaggio.
After the unnamed NASA space probe Infinity is pulled into a wormhole, it lands on a planet called Malgor, and is discovered by Zartog, a grumpy and wicked alien who likes to torture and kill animals for his amusement by dipping them in a substance called freznar, turning them into statues. From the probe, Zartog learns much about the culture of Earth, and wants to live like people. After discovering how to operate the probe, Zartog uses it to enslave the population and puts them to work, building his palace to resemble a casino. Those who resist are dunked into freznar, and decorated as statues in front of Zartog's palace.
When the Space Chimps (Ham III, Luna, and Titan) arrive on Malgor, Zartog makes his minions forcefully attack them, resulting in Titan's imprisonment along with their spaceship. Eventually, Ham and Luna rescue Titan and find their ship, only to be caught by Zartog and his minions. Zartog meets his defeat when Titan tricks him into pressing the eject mechanism of the Infinity probe, causing him to fall into the freznar and become a statue himself. Zartog, as a statue, is used by the chimps as support for their ship when they evacuate the planet using the force from the freznar volcano. Zartog falls off the shuttle when it enters Earth's atmosphere and presumably falls to his death.
Zartog Strikes Back
Zartog is revealed not only to survive the fall, but also become a lawn decoration for one of the NASA scientists. He eventually manages to free himself when the force of a rocket lifting off breaks away the freznar covering his body. He manages to raid the NASA base, determined for revenge against the chimps for depowering him, only to be caught by Titan. Being the dimwit he is, Titan allows Zartog into the headquarters as long as he doesn't touch anything. Not only does he break Titan's promise, he grabs his hands on a departiclizer remote and goes on a rampage, erasing the senator, scientists, and Kilowatt when she and Comet return to Earth. The chimps gain victory when Comet snatches the departiclizer from Zartog and uses it against him, before bringing everyone back to life. Zartog is also brought back shrunken and powerless, before being chased off by the same dog that peed on him at the beginning of the film.