Princess Azula (Chinese: 阿祖拉; pinyin: Ā Zǔ Lā) is a fictional character and the secondary antagonist in Nickelodeon's animated television series Avatar: The Last Airbender, and is part of the Avatar: The Last Airbender world. She was created by Michael Dante DiMartino and Bryan Konietzko, and voiced by Grey DeLisle.

In the show, Azula is the crown princess of the Fire Nation and an extremely powerful firebending prodigy. Upon Fire Lord Ozai's orders, she begins a quest with her childhood friends Mai and Ty Lee to retrieve her banished brother Prince Zuko and his mentor, their uncle Iroh, while also attempting to capture Avatar Aang, considered the Fire Nation's greatest threat to victory in the war. Azula is known for being a skilled strategist and a cold, calculating manipulator. She views weakness as failure, emotion as poison. As her brother Zuko states, she "always lies." Throughout the original series and the sequel comics, she is shown to be capable of highly advanced firebending, producing hotter blue flames as well as lightning.

Since she is the shadowed firebender in the series' opening sequence (though she is depicted bending red fire instead of her signature blue), Azula appears at the beginning of every episode of Avatar: The Last Airbender. In the first season, she makes her first appearance in a flashback during 13-year-old Zuko's Agni Kai (firebending duel) against their father, Fire Lord Ozai. Azula smirks as Zuko's face is burned after he refuses to fight Ozai, who takes this as a sign of weakness and disrespect. The Fire Lord then banishes the permanently scarred Zuko and tasks him with finding the long-lost avatar. Azula makes a second brief appearance at the end of the first season when Ozai tasks her with repatriating Zuko and Iroh, who accompanied his nephew into exile and briefly cooperated with the series' protagonists.

After her first attempt to capture Zuko and Iroh is accidentally thwarted by her ship's captain, Azula enlists the help of her childhood friends, Mai and Ty Lee. She eventually encounters the Avatar in Omashu and continues to pursue him, Zuko, and Iroh for the rest of the season. Following her initial failure to enter the Earth Kingdom capital Ba Sing Se using a giant drill to breach the city's strong outer wall, Azula comes in contact with the Kyoshi Warriors, esteemed fighters who, despite their lack of ability to bend any element, dress as and utilize the fighting style of Kyoshi, a past Avatar. Azula, Mai and Ty Lee then proceed to defeat and impersonate them.

Posing as Kyoshi Warriors, Azula and her friends infiltrate Ba Sing Se and befriend Earth King Kuei, who tells them about the planned invasion of the Fire Nation during an upcoming solar eclipse. Azula also comes to understand that the secret police and intelligence agency known as the Dai Li is the key to power in the capital. She is discovered as an infiltrator by Dai Li agents and brought before their imprisoned leader, Long Feng. Having in fact intentionally exposed herself, Azula lulls him into a false sense of control and accepts his offer to help stage a coup d'état against the Earth King and the loyalist Council of Five. Immediately after her seizure of power, Azula betrays Long Feng and assumes permanent leadership of the Dai Li. She also encounters Zuko in the city and convinces him to join her in order to redeem himself. During their showdown, Azula strikes Aang with a bolt of lightning while he is in the Avatar State, though he is later revived by Katara. Azula then orders the Dai Li to tear down the walls of Ba Sing Se, exposing the city to an invasion and occupation by the Fire Nation.

In the early episodes of this season, Azula bonds with her brother and friends after their victorious return to the Fire Nation with Iroh as a prisoner. However, Azula lies to Ozai by claiming that Zuko killed Aang, as she has a hunch that Aang survived and knows that all the blame would now fall on Zuko if this were true. During the two-part episode "The Day of Black Sun," Aang assembles an elite invasion force and attacks the capital, taking advantage of a solar eclipse that renders the firebenders powerless. Having been warned by Azula, Ozai is evacuated to an underground bunker prior to the invasion. Azula and her Dai Li agents stall Aang and his friends Sokka and Toph from finding Ozai before the eclipse, which lasts only eight minutes, allowing the firebenders to retaliate with full force once they regain their bending, causing the invasion to fail. However, Zuko defects to Team Avatar after confronting Ozai during the eclipse.

Later, Azula, accompanied by Mai and Ty Lee, visits The Boiling Rock, the top security Fire Nation prison where Zuko has been captured in an attempt to infiltrate the prison and rescue the captured forces of the failed invasion. However, Zuko, Sokka, Suki (leader of the Kyoshi Warriors, who had been captured in the aftermath of their battle with Azula) and Sokka's father Hakoda manage to escape. Mai betrays Azula by aiding the group's escape, proclaiming that she is doing so out of her love for Zuko. Enraged, Azula attempts to attack Mai but is stopped by Ty Lee, who renders her incapable of bending by blocking her chi (the energy within one which one would use for bending). After having Mai and Ty Lee imprisoned for betraying her, Azula follows Zuko and Sokka's group to the Western Air Temple, where she attempts to kill them. The fight ends in a draw, with Azula narrowly escaping death after falling from one of the airships while the protagonists manage to flee.

In the series finale, Azula intends to join Ozai as he sets out to conquer the world. Instead, he leaves Azula behind in the Fire Nation and names her as his successor to the Fire Lord position, though he does so only because he declares himself king of the world, effectively rendering the title of Fire Lord meaningless. Distraught by her father's abandonment and Mai and Ty Lee's betrayal, Azula sinks into psychosis, hallucinates about her long-lost mother, and deposes nearly all of her servants and advisers in fear of similar betrayal. Before she is crowned as Fire Lord, Zuko and Katara interrupt the ceremony, whereupon Azula challenges Zuko to single combat in an Agni Kai. However, Azula's attacks, while powerful, are wild and emotional while Zuko's are calm and disciplined; and when his attacks begin to overpower her, she sends a bolt of lightning toward Katara, but ends up striking down Zuko, who attempts to redirect it. She is ultimately defeated by Katara who freezes her in a block of ice, then handcuffing her to the ground before unfreezing her, causing her to have a mental breakdown.