Wan Shi Tong

History
Wan Shi Tong is the spirit of knowledge — an ancient and powerful being who knows more than any human walking the earth. He never misses a chance to learn a new fact, or to brag about his vast intelligence. Long ago Wan Shi Tong brought his library from the spirit world to the physical world. Together with his band of knowledge seeking foxes they collected knowledge from all over the world. He put it all on display in his library for humanity to read and hopefully better itself. Although he left his great collection of knowledge available to the mortal world for many years, he is recently rather angry at humankind; he apparently sees knowledge as something good purely for its own sake, and in recent years he is known to have been visited by humans only twice — once by Admiral Zhao (who was then a young lieutenant serving under "General Shu") and once by Aang and his friends — in both cases because the visitors were hoping to find secrets to destroying their enemies (the Water Tribes, and Fire Nation, respectively). Although his regular shape is that of an immense black-and-white barn owl, an animal commonly associated with wisdom in Western thought, he can lengthen his body to that of a huge serpent-like creature when angered. After Sokka breaks a vow made to Wan Shi Tong that no knowledge found in the library will be used for violence, Wan Shi Tong pulls the library back into the Spirit World before attacking Aang and the others.

Trivia

 * His name is a phrase in Mandarin Chinese ("萬知通") literally translates to "He Who Knows 10,000 Things."