Wan Shi Tong

Wan Shi Tong (AKA "He Who Knows Ten Thousand Things") is the Spirit of Knowledge in the world of Avatar the Last Airbender but is also cynical, xenophobic, and hostile to the Avatar, thus making him a villain despite his honest desire to preserve the knowledge he has accumulated. He is voiced by veteran actor Hector Elizondo.

Avatar the Last Airbender
Wan Shi Tong first appears in the second season of Avatar the Last Airbender in the episode "The Library". He oversees perhaps the greatest library in the world, but does not allow humans to enter based on the cynical belief that all humans who seek knowledge simply do so to gain some kind of advantage over an enemy. Though Aang and his friends are initially able to convince him otherwise, Sokka's going out of his way to locate a means by which to stop the Fire Nation enrages Wan. Ignoring the Gaang's pleas that the Fire Nation must be stopped, Wan Shi Tong decides to finish burying his library underneath the desert sands "so no one will abuse his knowledge again" before then trying to kill the Gaang on the grounds that they "know too much". Fortunately though, the Gaang manages to escape in time, but Professor Zei, who had spent his entire life looking for the library, chose to stay.

The Legend of Korra
Wan Shi Tong appears later in The Legend of Korra, his library now located in the Spirit World. He is leery of Jinora when she shows up asking for information on the Spirit Portals, and swiftly sells her out to Unalaq, who he has decided is a more "ture" ally to the Spirits than the Avatar.