Katara is a waterbending master, born in the Southern Water Tribe to Chief Hakoda and his wife Kya. During her childhood, she was the only waterbender living in the Southern Water Tribe. After losing her mother in a Fire Nation raid and her father left to battle against the Fire Nation in the Hundred Year War, she was raised by her paternal grandmother Kanna alongside her older brother Sokka. As a teenager, Katara and her brother discovered the young Air Nomad Avatar, Aang, who had been frozen in an iceberg with his bison, Appa, for a century. In need of a waterbending master, the siblings and Aang left the South Pole on a journey toward the Northern Water Tribe.

Realizing Aang was the Avatar, Katara and Sokka continued to travel with him across the world as he mastered the remaining elements, earth and fire. She became Aang's waterbending instructor after their departure from the Northern Water Tribe, replacing Master Pakku, who had instructed them during their time there. Her mastery of water made her a formidable asset to the group. The siblings' assistance helped Aang halt the Fire Nation's ambitions of world domination, ending the century-long war, and finally restoring balance to the world.

The murder of her mother and the later departure of her warrior father left Katara feeling traumatized and alone. Though she was cared for by Kanna, she invariably found herself filling the mother role left behind by Kya, even to her own older brother. Katara soon took on many of the responsibilities expected of an adult and quickly became independent and strong-willed. Morally and emotionally driven, she developed a great sense of justice and compassion for others, becoming fiercely protective of those in need.

After the Hundred Year War ended, Katara and Aang began a close romantic relationship that eventually led to marriage and raised a family with three children: Bumi, a nonbender who gained the ability to airbend later in life, Kya, a waterbender, and Tenzin, an airbender. Later in life, Katara became highly regarded as a master waterbender, and even said to be the best healer in the world. After Aang's passing, she became Avatar Korra's waterbending teacher and helped her to recover physically from her ordeal with the Red Lotus.