The Mooninites, Ignignokt (voiced by Dave Willis) and Err (voiced by Matt Maiellaro), are two pixelated, video game-like two-dimensional inhabitants of the Moon who see Earth primitive in every way, though they are frequently seen on it. Often the two come to Earth with selfish intentions to bug the Aqua Teens, namely Meatwad, usually taking advantage of his child-like innocence.
Ignignokt, the leader, is green and is larger than his companion, Err. Ignignokt usually is the one to come up with the Mooninites plans. Err is his hyperactive trash-talking tag-along. He often yells profanity to get his point across and usually agrees with anything Ignignokt says. Err has actually, however, sometimes shown he is the more intelligent of the two, despite his follower status.
Other Mooninites seen on the show include Uncle Cliff and the Gorgotron. Uncle Cliff is Ignignokt's uncle and screams over the slightest thing, an advantage that Err takes of. Cliff was a verteran of the Lunar War and gets "checks" from the government. The Gorgotron is a character featured in a video game set up by the Mooninites themselves for a scam. The Gorgotron says no with his foot.
The Mooninites have also mentioned that they do not have fathers and that they need attention, though this is likely untrue. They say that this is the reason they misbehave because they were never taught to "steal right" and etc. They use a purple, UFO-like and two-dimensional vessel to travel arround. Their ship shows some windows and can also deploy a ramp and landing legs.
Err fits precisely into Ignignokt's head; joining them together activates their superpower: they can fire a large square slow-moving easily-avoided video game "bullet" they call the "Quad Laser", which is a magnification of their smaller and faster (but still slow) laser attacks. A larger and more powerful version of this attack, the "Quad Glacier", seems to be barely moving to the naked eye.
So far, including the Spacecataz openers, the Mooninites have made nineteen appearances. If you count the movie, there are twenty appearances. Their latest appearence was in 2-and-a-Half-Star Wars Out of Five, as just a cameo near the end.

The Mooninites Wiki[aqua-teen-hunger-force.wikia.com]
Ignignokt and Err Quote Generator[www.live-evil.com]
ATHF at Adult Swim[www.adultswim.com]