Roku riding on Fang
Fang is the dragon Animal Guide who belongs to Avatar Roku. Him and Roku were incredibly close, sharing the same relationship as Aang with his animal guide, Appa or Korra and her animal guide, Naga. Fang was raised by Roku, who hatched the dragon egg himself, this could be one of the reasons why the two are so close.
He died with Roku, when both attempted to stop a huge volcanic eruption. His friend inhaled toxic fumes which knocked him down, Fang stayed with him the entire time resulting them both to perish in the volcano. In the spirit world, Fang appears blue rather than red which was his original colour.
Fang shows he can understand human speech easily but cannot talk back. When Aang managed to get into the spirit world, Fang arrived and contacted Aang by using telepathic images. These images are seen when his whisker touches Aang. He also does some gestures, such as nudging his head at a direction telling someone to look or go in that direction.