They are aliens from the fictional planet Rigel VII and appear almost exclusively in the Treehouse of Horror episodes. The duo has appeared in at least one segment of all twenty-five Treehouse of Horror episodes. Sometimes their appearance is the focus of a plot, other times a brief cameo. Kang and Kodos are often bent on the conquest of Earth and are usually seen working on sinister plans to invade and subjugate humanity.
In the episode “The Man Who Came to Be Dinner“, the Simpsons ended up on Rigel VII where Kang and Kodos give them a tour and a brief look at their lifecycle before placing them in a zoo with one of them, Homer, to be eaten in a yearly ritual. But after it is revealed that human consumption is fatal to their kind due to their unhealthy diet, their queen killed as a result, the Rigellans send the Simpsons back to Earth.
The first drawing of Kang and Kodos came from writers Jay Kogen and Wallace Wolodarsky. The finished design was based on an EC Comics issue cover. Kang and Kodos had brief cameo appearances in several non-“Treehouse of Horror” episodes and have appeared as villains in several of The Simpsons video games and as action figures.
The two also have a brief cameo in The Simpsons fun fair Ride. In 2013, a separate ride called Kang & Kodos’ Twirl ‘n’ Hurl was added in Universal Studios Florida park.
In 2009, Kang and Kodos were also made into 6″ collectible vinyl art toys by Kidrobot x The Simpsons. Kang was sculpted salivating and included an accessory book “How to Cook for Forty Humans”.