Kodos

Kodos is a Rigellian from Rigel 7. (S)he is the sister of Kang. It is unknown what gender Kodos is as he/she has been referred to as both male and female. 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, Kang has a deeper voice than Kodos.

Kang and Kodos once impersonated Bill Clinton and Bob Dole 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 were found out to not be welcome and fled from their primitive weapons.

Trivia
In the Ps2 game, Simpsons Hit &amp; Run, Kodos works with Kang to make an Intergalactic reality show in Springfield, Foolish Earthlings & is killed in the production due to the actions of Homer's plans of using nuclear waste to destroy the UFO.Kodos is an ailen.
 * Kodos has been referred to as both male and female. Female in Treehouse of Horror VII and male in Treehouse of Horror XVIII. Also, Kodos mentioned his/her "700 balls" in "Treehouse of Horror XVIII"
 * Matt Greoning had an idea about Kang and Kodos appearing on Futurama, but strangely they never did.
 * Kodos was confirmed to be female in a Simpsons Comic. However, since this is non-canon, his/her gender is still debatable.