Monk Gyatso was one of five head monks at the Southern Air Temple over 100 years ago. He was Aang's guardian and closest friend. He was a powerful Airbending master and, according to Aang, the greatest Airbender alive.
Gyatso was noted for his kindness and sense of humor. Even though his student, Aang, was training to be the Avatar, Gyatso believed that Aang should have time allocated for fun and games. Gyatso also had a strong friendship with the previous Avatar, Roku.
When the Fire Nation found a way inside the Southern Air Temple during the Air Nomad Genocide, Gyatso was killed. Gyatso did, however, go down fighting and took many Firebenders with him. A statue of him still stands in the Temple.
When Gyatso was young (and before he had become a master Airbender), Avatar Roku traveled to the Southern Air Temple to learn Airbending. Gyatso and Roku were close friends during this time (leading Roku's spirit to comment in "The Avatar and the Fire Lord" that some friendships are able to transcend lifetimes). In a glider lesson, Gyatso and Roku tried to beat each other in skill. Roku made loops, and Gyatso got on top of his glider and used it for air surfing (Aang, viewing this in flashback, claimed that Gyatso was a genius and that he had never thought about that). Gyatso soon loses control and is saved by Roku, who then crashes. Air was the second element that Roku learnt to bend.
Eventually, Gyatso became a master Airbender and was promoted to one of the five head monks at the Southern Air Temple. Monk Gyatso was highly respected, a great baker, kind, and very wise; but he remained a bit of a prankster. A statue of him was made in the Southern Air Temple. At some point, Gyatso also befriended a younger Guru Pathik, although the details of this are not known.
Twelve years after Roku's death, Gyatso was present when Aang was informed that he was the new Avatar, and Gyatso was appointed as Aang's personal teacher and guardian. He became something like a father to Aang, as well as a close friend and confidant. Gyatso helped Aang with his Airbending training, played games with him, and over all just made his time at the temple much better.
Even though Aang was training to be the Avatar, Gyatso believed that Aang should grow up as a normal boy. He refused to accelerate Aang's Airbending teaching, and ensured that Aang was content and had time for play. The other head monks disagreed with this, believing that Gyatso's compassion for the boy was clouding his judgment. They decreed that Aang was to be sent to the Eastern Air Temple. Aang overheard this and, having already been ostracized by his peers after his identity as the Avatar was revealed, was shocked that the monks wanted to isolate him from his last friend. Not realizing that Gyatso intended to fight this decision, so that he and Aang would not be separated, Aang fled the Temple with Appa and was subsequently frozen into an iceberg. Gyatso never saw Aang again.
Although the details are unclear, when the Fire Nation found a way inside the Southern Air Temple, they managed to kill Monk Gyatso and perhaps the other monks and airbenders as well. Gyatso did, however, go down fighting and took many Firebenders with him. A statue in his honor was placed in the entrance hall to the Southern Air Temple's inner sanctuary, and is still there.
- 'Gyatso' is the Tibetan word for "ocean", and is the name given to each incarnation of the Dalai Lama.
- Gyatso may have been a member of the Order of the White Lotus, as the Order Of the White Lotus has been around for a long time and he was shown to play Pai Sho with the White Lotus tile.
- It is possible that Gyatso is the shadowed airbender in the opening sequence.
- Gyatso is voiced by Sab Shimono, who also voices Master Yu.
- Near the end of the series, Aang is seen wearing beads that look exactly like Gyatso's.