Zuko was a Fire Nation royal and firebending master who reigned as Fire Lord from 100 AG until his abdication in 167 AG. He was the eldest child of Fire Lord Ozai and Princess Ursa. Originally the primary enemy of Team Avatar, Zuko devoted three years to trying to capture the long-lost Avatar to end his banishment and regain his honor as Crown Prince of the Fire Nation. He was recognizable by the distinctive burn scar on the left side of his face, which was inflicted on him by his father, Ozai, shortly before his banishment as a result of an incident in which he unintentionally disrespected his father by speaking out of turn and refusing to duel him.[20]

With support from his paternal uncle, General Iroh, and after much internal struggle and turmoil, Zuko grew disillusioned and rejected Ozai and his model of the Fire Nation. He instead joined the Avatar's group to become Aang's lifelong friend and firebending mentor[21] and was determined to end the war and restore both his and the Fire Nation's honor.[22] While Aang defeated Ozai, Zuko, with the help of Katara, defeated his younger sister, Princess Azula, and took his place as Fire Lord, declaring the end of the Hundred Year War and the start of a new era of love and peace.[15]

At the beginning of his reign, Zuko had to overcome great difficulties and solve several crises, especially those caused by the Harmony Restoration Movement[23] and the New Ozai Society.[24] Nevertheless, he succeeded in maintaining peace and eventually became one of the founders of the United Republic of Nations.[25] Zuko stepped down from his position as Fire Lord in 167 AG and became an ambassador of peace, relinquishing the throne to his daughter, Izumi.[12][26]Ozai was the ruler of the Fire Nation during the final years of the Hundred Year War, reigning as Fire Lord from 95 to 100 AG.[6] He was the second son of Fire Lord Azulon and Ilah, the younger brother of Iroh, uncle of Lu Ten, husband to Ursa, the father of Prince Zuko and Princess Azula, and the paternal grandfather of Izumi.[9] Ozai was a firebending master and, prior to the end of the war, was believed to be the most powerful firebender in the world.[10]

After his nephew, Lu Ten, died, Ozai usurped his brother's birthright to the throne[11] in a scheme that resulted in his father's death and Ursa's banishment.[12]

Ozai's rule saw a mass buildup of industry and significant technological advancements.[13] Like his father and grandfather before him, Ozai sought to conquer the other nations and become the supreme ruler of the world. To do this, he planned to utilize Sozin's Comet to burn down the Earth Kingdom, renouncing the title of Fire Lord and declaring himself the Phoenix King, ruler of the world.[14] Before his plans could come to fruition, he was defeated by Avatar Aang, who used energybending to remove his firebending abilities permanently. The war ended with his reign.

After the end of the war and Zuko's crowning, Ozai was sentenced to life in prison for several war crimes.[15] However, he was able to maintain a degree of influence on world politics through some of his loyal followers and his son, who occasionally sought advice from Ozai. As a result, the former Fire Lord was indirectly responsible for the failure of the Harmony Restoration Movement.[1][16]