Keef is very creepy.
Everything About Keef
In the episode Bestest Friend, Keef actually served as a main character. He was used by Zim as a best friend (due to his physical absorbency of liquids, shock-resistance, and ability to come out all right after an incident with a beaver and a taxi) so that Zim appears normal to the other Skool children. However, Zim soon tires of him following him everywhere, so he devises a plan to get rid of him; he sends him a package that contains robotic hands that rip out his eyes and replace them with robotic ones. After doing so, Zim hypnotizes him so that the first living thing he sees with his new eyes he will believe to be Zim. Unfortunately for Keef, the first creature he sees happens to be a squirrel. Enraptured, Keef chases the squirrel onto Zim's roof, where it finally attacks him, causing him to fall from the roof and seemingly explode.
Other than that early episode, Keef serves mainly as a background character, for example, in the Halloween Spectacular of Spooky Doom, he is seen in the nightmare world with the other monsters, but looks exactly the same. This is because, as Jhonen jokingly states "He was already scary enough to begin with".
He is voiced by Danny Cooksey. Keef is one of the few characters besides Zim to fully acknowledge GIR's presence, and even refers to him by name.
It was planned in Return of Keef for him to make another appearance, but due to the cancellation, the episode
was not complete. In this episode, Dib was going to use Keef to defeat Zim but failed. Even though this happened, Keef tried to get Zim and Dib to be friends (not knowing they hate each other.) Putting thier differences aside, Zim and Dib were to pretend to be friends to get Keef to blow up from happiness after being splashed with Zim's latest experiment. They succeeded, but once again Nickelodeon objected against killing Keef, so he would have eventually been revived somehow.