Considering the character's striking oddity, Wan Shi Tong, the owl spirit, was bound to make a return to the franchise one way or the other.

The wise, knowledgable, and frightening owl from Avatar: The Last Airbender made his second appearance in The Legend of Korra, along with his vast Spirit Library. The creature, Wan Shi Tong, has one of the franchise's most striking designs and it is therefore unsurprising that show creators found a place for him in the more mature sequel series.

Voiced by Héctor Elizondo, Wan Shi Tong's form is that of a white and black barn owl, although when angered or when hoping to intimidate his enemies, his shape morphs into a more monstrous version of himself. Obsessed with acquiring and amassing knowledge for centuries, the ancient being served as the caretaker of the Spirit Library, which he brought into the physical world before the events of Avatar: The Last Airbender. Aang, Katara, Sokka, Toph, and an eccentric scholar named Professor Zei stumbled on the library, and a suspicious Wan Shi Tong admitted them with the condition that any knowledge gained on their visit would not be used for violence. However, when Sokka accidentally reveals that the Aang Gang is indeed looking for ways to defeat the Fire Nation, the owl reacts harshly, chasing the adventurers from the library as he buries it (with Professor Zei still inside), and returning to the Spirit World.

Though it was assumed that Wan Shi Tong and his Spirit Library were lost forever, both returned in The Legend of Korra season 2, episode 10 "A New Spiritual Age." After a century since his last interaction with humans (poor Professor Zei is revealed to have died after the edifice sank), the owl-librarian still inhabits the Spirit World, having apparently grown increasingly uneasy around humans since his last interaction. When Aang's granddaughter Jinora, looking for ways to locate existing spirit portals on Earth, finds her way to the place and, despite his initial reluctance, Wan Shi Tong permits her to stay and look through his collection.

By the end of the episode, its is revealed that Wan Shi Tong — apparently still upset over his experience with her grandfather — has only allowed Jinora to stay in order to turn her over to Unalaq, who seeks to unlock the evil spirit Vaatu. Once the plot becomes clear to her, the owl announces to Jinora that he has no more need of humanity nor its frivolous inventions, and declares his previously-formed allegiance to Unalaq. According to Wan Shi Tong, the waterbender was a "true friend" to spirits, but just what he knows of Unalaq's "Dark Avatar" plan and it's Spirit World ramifications is unclear.

The owl — an animal that symbolizes wisdom in many cultures — has access to  seemingly endless knowledge, yet his own paranoia and inability to see the nuance of the human experience has been shown to bring about cruel action (i.e. Professor Zei's death and Jinora's betrayal). Furthermore, his alignment with Unalaq in The Legend of Korra seems like a miscalculation on his part, as Unalaq, a human, manages to corrupt his spiritual brethren by turning them dark — an outcome that certainly goes against the spirit's desired isolation from humanity. Even with all the knowledge in the world, one can still make the wrong choices when failing to empathize with others and see their larger picture.

Both Avatar: The Last Airbender and The Legend of Korra are noted for their inclusion of rather heavy and dark subject matter into what are ostensibly a children's cartoons. Considering the character's striking oddity and his unresolved plot from the original series, Wan Shi Tong was bound to make a return to the franchise one way or the other. Perhaps he will find a new way of antagonizing the next Avatar on their quest of bringing balance to the world.

Next: Legend of Korra's Original Plan Would've Properly Ended Avatar's Story