Nibbler

Lord Nibbler (voiced by Frank Welker) masquerades as an innocent, cute and unintelligent pet during most of the series. In reality, he is highly intelligent and capable of communication, but tries to avoid suspicion while he goes about his mission of protecting the Earth in general and Fry in particular from the evil Brainspawn. Nibbler's feces consist of dark matter (as all of his species do), which can be used as starship fuel. It is an extremely dense material, "each pound of which weighs over ten thousand pounds", according to Professor Farnsworth.