"You think you're any different from me, or your friends, or this tree? If you listen hard enough, you can hear every living thing breathing together. You can feel everything growing. We're all living together, even if most folks don't act like it. We all have the same roots, and we are all branches of the same tree."
— Huu to Team Avatar.
Huu was a waterbending master native to the Foggy Swamp Tribelocated southwest of the Earth Kingdom. Huu reached enlightenment while sitting under the great banyan-grove tree in the heart of the swamp. Huu, being the wisest member of the tribe, believed that all living things were connected to one another. Having been so connected to the swamp, Huu made it his duty to behave as the guardian of it, protecting it from those who intend to harm it, while disguised as a swamp monster, made possible only through his exceptional "plantbending" skills, the ability to bend liquids in plants to manipulate them. Despite the apparent lack of political structure in the swamp, other swamp waterbenders appeared to respect him and consider him a leader.
When a freak tornado caused Team Avatar to crash into the swamp, the team was separated. Huu, in the form of a plant monster, attacked them, not knowing Aang was the Avatar and wanting to protect the swamp from the machete-wielding Sokka. Aang and Katara immediately came to Sokka's aid, but the two benders had some trouble defeating the "monster". Huu entrapped Sokka in the vines and threatened to engulf him completely, but Katara used her ice breath to freeze the water in the vines ensnaring Sokka and used a powerful stream of water to free him completely. Huu's identity was eventually revealed when Katara sent numerous water slices at the monster in rapid succession, too quick for Huu to gather more vines in order to maintain his disguise. With one final slice, Katara severed the wooden board that served as the monster's face, revealing that the monster was Huu all along.
Upon learning of Aang's identity as the Avatar, Huu invited Aang and his friends to accompany him to the banyan-grove tree, located in the center of the swamp. Once they arrived there, he taught the trio about the connection of all living things in the world, saying that "[they] all [had] the same roots, and [they were] all branches of the same tree." He explained that the swamp "told" people that they were still connected to their loved ones that had died, that "time [was] an illusion, and so [was] death". Due to Huu's lesson, Aang was able to use the connections in the swamp to track down Appa and Momo from whom they got separated after the storm.
Huu was part of the "ragtag team of friends and allies" that was going to assist Team Avatar in the Invasion of the Fire Nation. When the battle on Fire Nation shores started, Huu was nowhere to be found, arousing some concern amongst the other Foggy Swamp Tribe members. He appeared moments later, covered in seaweed, to recreate the "swamp monster". He excused himself of being late, stating that it had taken a long time to collect enough seaweed for his swamp monster disguise.Tho, Due, and Huu helped with the initial land stage of the invasion, but remained behind to protect the waterbending-powered submarines while the invasion force began to scale the volcano.
When the eclipse ended, the Fire Nation deployed their airships to bomb the submarines on the beach. The Foggy Swamp waterbenders destroyed as many bombs as they could in an effort to protect the subs, but could not keep up with the multitude of explosives raining down upon them. Huu was nearly killed when one of the bombs slipped through the seaweed and exploded, but he peeped out of the smoking seaweed moments later, seemingly unharmed. Huu, Tho, and Due survived the attack, but the submarines were completely destroyed in the process, cutting off the invasion force's only way to retreat. They were imprisoned with the rest of the adults of the invasion force.
Huu was a master waterbender who specialized in the sub-skill of plantbending: bending the fluids inside the highly saturated plants of the swamp. He mastered this technique to the point that he seemed to be bending the vine itself. Covering his body with these vines, Huu pretended to be a large swamp monster in order to scare away anyone who wanted to harm the swamp. This technique strongly resembled bloodbending.
During the invasion, due to a lack of vines near the Fire Nation Capital, Huu instead covered himself in seaweed. His "plant suit" was strong enough to easily throw and smash tundra tanks. It also proved a good defense against fire attacks, but could not withstand an explosion from the inside.
The manner of how Huu gained enlightenment by sitting under the great banyan-grove tree may have been a reference to Siddhartha Gautama and how he sat under a Bodhi tree to achieve enlightenment and became the Buddha. His belief that all beings are one is similar to the Buddhist doctrine of Non-Duality and his corresponding guardianship of the natural world are consistent with Taoist teachings.
Hữu, pronounced like who, is a Vietnamese name written as 友 in Chinese, meaning "friend" or "friendly".
The philosophy Huu espoused, the notion that all things are connected and the entire planet is a single organism is the Avatar World version of the real-world Gaia Hypothesis.