"Let me tell you, Sokka, I've courted a lot of girls, but Yue is the finest and she comes with the most perks. I mean, Yue's nice and everything, but the points I'll gain with the chief aren't bad either."
— Hahn to Sokka in "The Siege of the North, Part 1".
Hahn was a slick, career-minded soldier who resided in the Northern Water Tribe, and was solely focused on the Hundred Year War. Due to Hahn's high ranking, ChiefArnook arranged a marriage between the soldier and PrincessYue. However, this marriage never took place due to Yue's death. Often considered by women as the handsomest warrior in the Northern Tribe, Hahn preoccupied himself with making a good impression on his superiors.
Although he was not a waterbender, he showed skill in handling a variety of weapons and was a respected warrior, having been chosen to lead a secret attack on the Fire Navy's commanding officer during the Siege of the North. These skills, however, were not as impressive as he thought them to be, as during the mission, Hahn was unable to effectively attack the fleet's commanding officer, AdmiralZhao.
Hahn was arranged to be married to Princess Yue prior to the latter's sixteenth birthday. He was not opposed to the idea, even though Yue did not appear to have a romantic interest in him. He did not seem to like her much either, but was more interested in the ideas of becoming royalty and the "perks" it would allow him to have by being related to the chief.
As the Fire Nation began assaulting the Northern Water Tribe, Hahn volunteered himself for a mission to attack the invaders. In the process he became acquainted with Sokka and developed a strong disregard for him. Sokka immediately recognized Hahn's shallowness and his lack of love for Yue, and therefore did not act respectfully toward him. Hahn mocked Sokka for being a mere Southern Water Tribesman and for his concern over his engagement to the tribal princess. The two physically fought each other when Sokka's hatred for Hahn boiled over, resulting in Sokka being relieved from his duties; however, Hahn showed no remorse whatsoever for the altercation.
Hahn's secret mission to ambush the attacking Fire Nation fleet's admiral ended rather abruptly. Disguised in an old Fire Nation military uniform and having infiltrated Zhao's ship undetected, he planned to attack the admiral. However, rather than stealthily sneaking up on Zhao, Hahn revealed his identity, shouted to the commanding officer, whom he again mistakenly called "Choi", and charged at him. Without interrupting his conversation, Zhao hurled him overboard.
Hahn was self-centered, egotistical, and conceited with a deep desire to gain a higher political rank. He was somewhat ignorant, due to his engrossment in himself and rarely thought twice about his actions, which subsequently led to his defeat at the hands of Admiral Zhao. He seemingly enjoyed mocking Sokka by consistently talking of his engagement to Yue, irritating Sokka deeply. Hahn's known interests included sharpening his weapons, courting girls, and ensuring his hair looked good. He was terrible at remembering names.
Hahn proved himself incapable of correctly pronouncing certain names, mistakenly saying Admiral Zhao's name as both "Admiral Choi" and "Admiral Cho", and Sokka's name with a long "O", as it was later pronounced in the live action film.
The tension between Hahn and Sokka represented a clash between the two separate cultures of the two Water Tribes: Sokka was initially uneducated and cared less for beauty and culture and was a more simple, humble and scientific warrior, while Hahn was deeply immersed in his culture and perceived marriage as no sacred thing borne of love (as Sokka might believe) but a political necessity required to ensure the tribe's survival.
Apparently, Hahn courted several girls before his engagement with Princess Yue, but stated Yue is the finest and "comes with the most perks", much to the annoyance of Sokka.
Hahn is one of the few members of the Water Tribe who does not have the sound "uh" in his name.