Kang

Kang Johnson is a Rigellian from Rigel 7. He and his sister Kodos continuously try to take over Earth and are usually seen attacking Springfield.

Kang and Kodos have a lot of space weaponry at hand and have their own spaceship. They speak the Rigellian language, which, by coincidence, is identical to English. Although they look identical, Kang has a deeper voice than Kodos.

History
Kang once impersonated Bob Dole in order to become President of the United States, in Treehouse of Horror VII's Citizen Kang/Mr. Kang goes to Washington. When Kang was revealed to be an alien, he was still more popular than a third party.

In Treehouse of Horror IX's "Starship Poopers," it is revealed that Kang is Maggie's father after probing Marge with an insemination ray for a cross-breeding program, which resulted in Maggie growing alien legs and an alien tooth (this is non-canon).

Kang and Kodos have both ruled over Springfield until they were found out to not be welcome and fled from their primitive weapons.

The Simpsons Game
Kang (along with Kodos) appears at the end of Mob Rules, when they cause Dolphins to attack humans, cause Lard Lad to assault the industrial zone of Springfield, and invade the mall. However, when they were thwarted, they decided to start attacking Springfield. This causes the Simpson family to enter the game engine to find the creator, but Groening wasn't enough to defeat the aliens because he didn't want to. Soon after God is defeated, God decides to replenish Springfield, returning peace to the city.