"I love you three too much! I don't know what I would do if I lost you, Zuko, Maya or Azula! You three are my guiding light, and it would kill me to let you go..But if that's what it takes to keep you all safe, then so be it."

— Ozai accepting the fact that he may have to die to keep his children safe.

Ozai Northuldra (née Hira'a) is a noble and the current incarnation of the Avatar, the manifestation of the world in human form, and thus the only person in the Avatar world who can use all four bending disciplines: Airbending, Waterbending, Earthbending and Firebending as well as being one of the few Avatars to learn Energybending, and the only one to use it during the story. He is the immediate Avatar successor of Princess Kalika and the Fire Nation Avatar succeeding Roku. So far in history, he is the only Avatar to bend metal, blood, and lava.

He is the only son of Aiden and Serafina Hira'a, the maternal grandson of Roku and Melody Hira'a, and the great-grandson of Kuruk and Kamaria. While Ozai was married to Ursa, he bore two children: son Zuko and daughter Azula. After their relocation to the Southern Water Tribe, Ozai courted and later married Bato and had two daughters: Maya and Melody, the latter of whom was named after his grandmother. By the end of the Hundred-Year-War, Ozai was the mother-in-law of Sokka and Katara Pathuk, and the grandmother of Saoirse, Kiara, Amaya, and Kida. He was also the adopted mother of Toph Beifong after the disownment and death of her parents. Formerly the consort to the Fire Lord, Ozai married Ursa out of fear and for the safety of his people.

Ozai is also one of the only characters to come from a lineage of Avatars, one from the Water Tribes and the other from the Fire Nation. When his son and daughter were ten and eight years old respectively, his wife, Ursa, murdered her father by slipping poison into his tea and crowned herself Fire Lord, effectively stripping of his title and birthright. Ursa's first act as Fire Lord was banishing him, Zuko, and Azula, and they weren't allowed to return unless they found the Avatar. But what Ursa didn't know, was that Ozai is the current incarnation of the Avatar, and it was a secret that only he and his children knew.

Under the cover of the night, the three slipped onto a boat and escaped to the . Once arriving on the frigid continent, they managed to make their way to the main village; there, the small family met , his wife, Kya, and his two children, and . Over their first three years in the village, after settling down, Ozai took a romantic interest in , Hakoda's best friend. And after three years of dating, the two eventually married, with Zuko and Azula gaining a father that they deserve, and Ozai becoming pregnant with his and Bato's daughter.