Momo from Avatar: The Last Airbender originally had a different name and design. In the show, Momo is a flying lemur who joins Team Avatar in season 1, episode 3, “The Southern Air Temple.” Aang, Katara, Sokka, and Appa visit the Southern Air Temple to help Aang reconnect with the Air Nomads and Momo appears while the gang is exploring. A famished Sokka begins to hunt Momo while Aang also chases Momo to try and befriend him. In the midst of the chase, Aang stumbles upon the remains of his friend and mentor, Monk Gyatso, and is so distraught that he inadvertently enters the Avatar State. After Katara helps to calm him and the dust settles, Aang says to Momo and his flying bison, Appa, “We’re all that’s left of this place.”
But Appa and Momo share more than their native habitat with the Air Nomads — the designs for Appa and Momo were inspired by two characters from the same film. Appa is partially based on Catbus from My Neighbor Totoro while Momo was influenced by the character of Totoro himself. Momo is primarily a hybrid of lemur, bat, and co-creator Bryan Konietzko’s childhood cat, “Buddy,” but Konietzko wanted to dial up Momo’s cuteness as much as possible, so he looked to Totoro's exaggerated features for inspiration. Yet the earliest designs for Momo resemble neither Totoro, cat, lemur, nor bat.
In the book Avatar: The Last Airbender - The Art of the Animated Series, Konietzko explains that Momo was originally “a little robot, a cyclops monkey,” which is something that might have fit in the steampunk-inspired world of Avatar: The Legend of Korra, but not so much in The Last Airbender. Momo was previously Momo-3, a mischievous robot monkey who was the relic of an ancient, industrialized civilization. When the world of Avatar was changed to be less futuristic, the creators of the show decided that — rather than discarding the character of Momo altogether — they could redesign him to fit in with the pre-tech universe they had settled on for Avatar.
Momo-3 carried a staff and had the shape of an arrow on his head which became Aang's blue arrow tattoos and flying staff. Then, Momo-3 became Momo, a flying lemur with large, pointed ears, a long tail, and retractable wings. At one point, the creators thought to have Momo be a reincarnation of Monk Gyatso, but that idea was scrapped. And because they thought it would have been improbable that Aang, Appa, and Momo were all frozen in the iceberg together, the creators decided to have Aang find Momo at the Southern Air Temple. In the show, Momo gets his name when he steals a peach from Sokka and Aang calls the flying lemur “Momo” – meaning “peach” in Japanese. From that moment on, Momo is a part of their family.
As an animal companion to Team Avatar, Momo is sometimes an asset to the group, but more often he is comic relief. The flying lemur is usually up to some hysterical antics, whether it’s overstuffing himself with fruit to the point that he can no longer fit through a vent or bringing Katara the wrong thing (multiple times) after she asks him to get water. Momo also develops a close friendship with Appa and the two are often seen together, seemingly able to communicate with each other. But above all, throughout Avatar: The Last Airbender, Momo is a symbol of hope for Aang. While Aang learns that he is, indeed, the last airbender, he finds hope in the connection that he shares with Appa and Momo.