Master Pakku was a Northern style waterbending master and instructor who possessed immense skill and power, and was once regarded as the best waterbender in the world. Dryly sarcastic and very serious about his art, he was a harsh, but nonetheless effective teacher, as well as an outwardly acerbic yet inwardly caring old man. Adhering to the Northern Water Tribe traditions, he exclusively taught waterbending to male students; however, he made an exception for Katara, his ex-fiancée's granddaughter. Due to his great waterbending skills and wisdom, Pakku was also a member of the Order of the White Lotus, taking part in Ba Sing Se's liberation.
Born to a long line of waterbending masters, Pakku began training as a waterbender "before he could stand", quickly advancing to become a master himself.
In his youth, Pakku was a talented waterbender, and, by way of arranged marriage, became engaged to Kanna, a Northern Water Tribe girl of similar age. He had deep, genuine feelings of love for Kanna; however, she did not reciprocate these, mostly due to his support of the tribe's patriarchal traditions. Unable to face her fate, Kanna fled to the Southern Water Tribe. Pakku was devastated by this turn of events; however, he refused to admit that it was his stubborn insistence on customs that caused him to lose the love of his life. He soon became malcontent and cranky, converting the pain of his loss into callousness toward others, thus denying himself the hurt of Kanna's betrayal. Over the years, Pakku became the leader of his tribe's waterbenders and led them to serve as the Northern Tribe's first line of defense against the Fire Nation.
Years later, when AvatarAang and Katara arrived at the Northern Water Tribe in search of a master from whom they could learn waterbending, Pakku consented to instruct him. However, as per the tradition of the Northern Water Tribe that only men were to be allowed to learn combative waterbending, he rejected Katara as a pupil and sent her to learn healing instead. Aang began training Katara at night, passing on what he had learned with Pakku, but within minutes they were discovered by the master himself, and for his disrespect, he barred Aang from further instruction. Knowing that Aang could not afford to waste the opportunity to learn from Pakku for her own sake, Katara pleaded with the Chief of the Northern Water Tribe, Arnook, to persuade Pakku to take Aang back as his student. By suggestion of Arnook, Katara was about to apologize to Pakku, but changed her mind at the last minute, unable to submit to Pakku's sour chauvinism. Katara, in defiance, challenged Pakku to a duel. Though he initially had no intention of accepting, Pakku eventually fought Katara. She was easily outmatched by the master, but refused to give up. Pakku ended the duel by trapping Katara among spikes of ice. Though he acknowledged her apparent skill, Pakku still would not consent to teach her.
During his fight with Katara, Pakku knocked her grandmother's necklace to the ground. Picking it up after the duel was finished, he recognized its pendant as the betrothal necklace he had carved sixty years before for "the love of his life", his fiancée, Kanna. Realizing that his stubborn adherence to custom had cost him a wife, Pakku consented to teach both Aang and Katara, the latter learning and improving faster than any of his students. After this, Pakku played a critical role in defending the North Pole in the Siege of the North. Following the battle, Pakku tasked Katara with instructing the slower-learning Aang, and also decided to travel to the Southern Tribe to help them rebuild their nation.
Aang and his comrades accompanied Pakku at the beginning of his journey to the Southern Tribe before separating to travel to Omashu. When the groups split, Pakku gave Katara a vial of water from the Spirit Oasis in the Northern City and gave Aang a box containing scrolls of waterbending techniques. As for Sokka, Pakku gave him only words of good luck, to Sokka's disappointment. Pakku and the other Northern healers and waterbenders worked to restore the war-torn Southern Water Tribe, where he reunited with Kanna and finally married her, even making her a new betrothal necklace.
When he and the other Order of the White Lotus members received a message from Iroh, Pakku joined the effort to liberate Ba Sing Se. Shortly before the arrival of Sozin's Comet, the Avatar's group reunited with Pakku and their other teachers who were in the Order of the White Lotus. When Katara and Sokka saw him, he told them that he was their new grandfather, as he had finally married Kanna while he was away. The two children were thrilled with this development. Sokka tried to find a nickname of his liking, considering "Gramp-Gramp" and "Grampakku", much to Pakku's annoyance, but was unable to create a good one. Pakku then told his step-grandson to "just call him Pakku", and Sokka's face fell as he was again dismissed by his step-grandfather.
Pakku and the Order of the White Lotus launched an attack on Ba Sing Se, working to liberate the city during the arrival of Sozin's Comet. Pakku created a large waterslide over one of Ba Sing Se's walls, distracting Fire Nation soldiers. He then froze the slide, trapping the soldiers and allowing himself and Piandao to slide into the city. He initially blocked a large fire blast, but the flames evaporated the water, leaving him unable to defend himself from a second blast. Fortunately, Jeong Jeong intervened and dissipated the blast. Following the successful liberation, Pakku joined his allies and family at Zuko's coronation.
Pakku was a waterbending master, among the best in the world along with Katara and Hama. He was the Northern Water Tribe's waterbending instructor. During his duel with Katara, he created very large waves of water and ice. He eventually defeated Katara by trapping her in ice spikes thrown down at her from the air, which he was able to guide each perfectly to trap her without hurting her. During the Siege of the North, Pakku, empowered by the full moon, held his own against dozens of soldiers with his enhanced waterbending, creating an extremely large water spout. His skill, and the methods through which he trained his students, played a large part in helping Katara to become a waterbending master.
During the Liberation of Ba Sing Se, Pakku fought many comet enhanced Fire Nation soldiers alongside Piandao by creating a large wave and then freezing it, allowing the swordsmaster to slide down on it and disable the soldiers. He, along with the rest of the Order of White Lotus, successfully liberated Ba Sing Se.
He also had some considerable skill in unarmed combat, easily shattering Katara's ice disk assault with his barehanded chops. In addition, he was able to dodge most of her attacks, proving to be quite agile in combat even for his old age, and he was able to counter-attack proficiently.