Koori Kumo is the great-great-great-great grandson of Avatar Aang and Katara, master waterbender. An white-haired aspiring waterbender residing in the Northern Water Tribe, Koori favors the technique of ice-bending frozen boomerangs in the likeness of Sokka, another distant relative from the past. He has always felt a deep connection to his family and the generations before him. As a teenager, Koori was given a necklace by his grandmother, which once belonged to Katara. Traditionally, the eldest daughters in his family would be "offered to the moon" and thus had white hair. However, since Koori's mother had no daughters, he was given this distinction. He is a close friend of his cousin Ame Suiki, whom he went with to spy on the Waterbender Army on the day of the Southwest Storm.
Like his ancestor Katara, Koori has a modest, marginal sense of humor. His outgoing attitude complements his adventurous spirit. Being descended from the last Air Nomad Avatar, Koori has always identified himself strongly according to his heritage.