Appa (Chinese: 阿柏; pinyin: Ā Bǎi) is a fictional character on the Nickelodeon animated television series Avatar: The Last Airbender and in the film The Last Airbender.In the series, Appa is the only known living sky flat-tailed flying bison , a species of animals that can fly naturally, and is the animal spirit guide of the protagonist, Aang.