Kodos

Kodos (pronounced Koh-dohs) is a Rigellian from Rigel 7. She is the sister of Kang. The duo usually appear in Treehouse of Horror episodes. Together, Kang and Kodos try to take over Earth and are usually seen attacking Springfield.

Kang & 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, Kodos has a higher voice than Kang.

History
Kang and Kodos once impersonated Bob Dole and Bill Clinton respectively in order to become elected President of the United States. When they were revealed to be aliens, they were still more popular than a third party.

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

Kodos acted harmless to Bart while her plan was to activate the beacon to call the other Rigellians including Kang but earth got the upper hand and she failed [4].

The Simpsons Game
Kodos (along with Kang) 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 are thwarted, they decide to start attacking Springfield. This causes the Simpson family to enter the game engine to find the creator, but Groening isn't enough to defeat the aliens because he doesn't want to. Soon after God is defeated, God decides to replenish Springfield, returning peace to the city. Kodos is male here.

Trivia

 * Kodos has been referred to as both male and female. Female in Treehouse of Horror VII and male in Treehouse of Horror XVIII, though this may be due to humans being unable to tell male and female Rigellians apart. Also, Kodos mentioned his/her "700 testicles" in "Treehouse of Horror XVIII", however, in Treehouse of Horror XXII, Kamala, a female Rigellian, also made a reference to having testicles.
 * In several DVD commentaries, Matt Groening and other writers confirm that Kodos is indeed written as female, as consistently as possible.
 * Matt Groening had an idea about Kang and Kodos appearing on Futurama, but strangely they never did. However, they did appear in the Simpsons-Futurama cross-over episode "Simpsorama", where Kang and Kodos are both depicted as females.
 * In the video game, Simpsons Hit &amp; Run, Kodos works with Kang to make an Intergalactic reality show in Springfield, Foolish Earthlings and is killed in the production due to the actions of Homer's plan of using nuclear waste to destroy the UFO.
 * In the Family Guy/Simpsons crossover "The Simpsons Guy", it is revealed that Kang and Kodos went to summer camp with Roger the Alien from American Dad.
 * Kodos is Jewish, according to Treehouse of Horror XVIII.