Pakku is a master Waterbender and uses a lot of dry sarcasm. Born and raised in the Northern Water Tribe, Pakku is very set in his culture's traditions. He also takes his waterbending classes that he teaches very seriously; the classes start at sunrise, and not even the Avatar receives special treatment or gets a break. Pakku also has a rather sexist attitude towards women and where they 'belong'.
Over 60 years ago, Pakku was in an arranged marriage with Katara's Gran-Gran, Kana. Following the tribe's tradition, he carved a symbol (Waterbending) onto a charm necklace and gave it to her as a sign of their engagement. Although Pakku loved Kana very much, and was certain that they would have a long, happy life together, Kana did not feel the same. So she fled to the Southern Water Tribe without even saying goodbye to her friends, although she kept the necklace with her.
This necklace was passed on to Gran-Gran's daughter, which was eventually passed down to Katara. Actually, it is probably because of this necklace that Pakku finally agreed to teach Katara waterbending. Before, Pakku refused to teach her because of his tribe's tradition that women weren't allowed to learn waterbending. This combined with his irkable attitude caused Katara to call him out to fight. And while her waterbending skills did impress him, he still wouldn't teach her because she was a girl. But soon after he found Katara's necklace and when he learned that she was Kana's granddaughter, he changed his tune. Now he is teaching both Aang and Katara the proper methods of Waterbending.