El Chupanibre

El Chupanibre is a sewer monster who once terrorized the mutants below New New York. He is a giant green humanoid lizard with massive yellow teeth and claws. He was flushed down a colossal toilet to the sub-sewer by Bender in the course of saving Nibbler. But in later episodes, he is seen back in the regular sewers.

It can be inferred that El Chupanibre might once have been a common animal or even human that was transformed into its current shape via the mutagenic properties of the sewage.

Trivia

 * The name "El Chupanibre" is a play on the Puerto Rican and Mexican myth of El Chupacabra, which means "the goat-sucker". The monster supposedly sucks the blood of goats and other livestock. However, the suffix "nibre" is gibberish, so the name "Chupanibre" has no direct translation.