Sozin's Comet: The Final Battle is the series finale for the Nickelodeon television series Avatar: The Last Airbender. It was directed by Ethan Spaulding, Giancarlo Volpe, and Joaquim Dos Santos, and written by Michael Dante DiMartino, Bryan Konietzko, and Aaron Ehasz. Though intended to be split into three parts, the finale aired as a two-hour four-part movie on July 19, 2008. Prior to the week of July 14–19, no episodes had been shown since November 30, 2007 The Saturday airing of Sozin's Comet acted as a climax to a week of ten new episodes that concluded Avatar's third season.

The finale focuses on series protagonist Aang's non-violent personality and his reluctance to kill Fire Lord Ozai. The finale also follows the exploits of many of Aang's friends and allies, including Sokka, Toph and Suki's struggle to destroy a Fire Nation airship armada, Zuko and Katara's battle against Zuko's sister Azula, and Iroh, King Bumi, and the Order of the White Lotus' attempt to reconquer Ba Sing Se.

Sozin's Comet received positive reception from critics and fans alike. The initial showing averaged 5.6 million viewers, a 195% increase in ratings compared with ratings from mid-July 2007. The premiere of episodes 52–61 throughout the week of Sozin's Comet's release received over 19 million views, of which 5.6 million were from the premiere of Sozin's Comet. At the 2008 Annie Awards, the director of the third part of Sozin's Comet won an award for "Best Directing in an Animated Television Production".

Part 1: The Phoenix King

Aang suddenly abandons his Firebending lesson with Zuko to have a beach party, causing Zuko to attack him in his frustration. Aang explains he plans to challenge Fire Lord Ozai only after Sozin's Comet and its enhancement of Firebending have come and gone, due to his own self-perceived lack of Firebending skills at the moment. When Zuko tells the group Ozai plans to use the comet's power to burn down the Earth Kingdom, Aang resolves to face him before the comet arrives. Sokka decides to have a simulation fight against a scarecrow, but Aang refuses to kill it due to his pacifistic nature and non-violent upbringing,[8] and even berates his friends as they tell him that he must eventually kill Ozai.

That night, Aang sleepwalks to a forest not to be found in the morning. After the group fails to locate him, Zuko takes them to June, a tracker who might be able to locate Aang. Meanwhile, Fire Lord Ozai proclaims himself to be ruler of the world, under the title "Phoenix King", and declares Azula to be the new Fire Lord, setting off to burn the world and rebuild it under his New Order.

Part 2: The Old Masters

Zuko's tracker, June, is unable to locate Aang, but does find Zuko's uncle, Iroh. He and several other characters (Katara's Waterbending master Pakku, Aang's first Firebending instructor Jeong Jeong, Aang's Earthbender friend King Bumi, and Sokka's swordmaster Piandao) are part of an otherwise non-aligned group known as the "Order of the White Lotus", which plans to liberate the Earth Kingdom capital, Ba Sing Se, from Fire Nation rule. Zuko and Katara decide to fight Azula in the Fire Nation capital while Sokka, Toph, and Suki attempt to destroy the airship fleet.

Meanwhile, Aang awakens on a floating island. Frustrated with his inability to find a way to defeat Ozai without killing him, he asks four of his past lives for advice. Unsatisfied with their answers, he asks the island for help. The island, which is actually a giant "lion-turtle", provides Aang with the power of energybending and leaves him on the Earth Kingdom shores.

Part 3: Into the Inferno

The Comet appears in the sky, and Azula's coronation takes place. Azula banishes nearly all of her subjects (including her Dai Li agents) in fear of betrayal. Her paranoia and loneliness begin to drive her insane. Before she is crowned, Zuko and Katara arrive. Zuko accepts Azula's challenge of an Agni Kai, or "fire duel", because he feels that something is wrong with Azula and he does not want Katara injured. Just as Zuko is on the verge of defeating Azula, she shoots a bolt of lightning at Katara instead of Zuko. Zuko throws himself in front of her and intercepts the lightning, preventing Katara from getting hurt, but he gravely injures himself after he fails to correctly redirect the lightning.

Meanwhile, Sokka, Toph, and Suki hijack a Fire Nation airship, and use it to destroy many others, effectively stopping Ozai's plan of incinerating the Earth Kingdom. In Ba Sing Se, the Order of the White Lotus, led by Iroh, lay siege to the Fire Nation forces within the city, with the sole intention of re-conquering it in the name of the Earth Kingdom. Aang reappears and begins to duel the Fire Lord. However, when Aang successfully redirects lightning he purposely misses Ozai to avoid killing him. Because of his pacifism, Ozai begins to gain the advantage.

Part 4: Avatar Aang

Zuko lies on the ground twitching as Katara and Azula fight. After several minutes of running, Katara freezes Azula and chains her to the ground. Upon reaching insanity, Azula cries frantically and breathes blue fire out of her mouth. Katara then revives Zuko.

After a fierce battle, Ozai slams Aang into a rock, hitting the scar on his back from Azula in the previous series, inadvertently releasing his locked seventh chakra and making him enter the Avatar State. With the power of his past lives, Aang overwhelms Ozai. Although Ozai is subdued, Aang refuses to kill him; instead, he locks Ozai down with earth. He realizes what the lion-turtle had meant and uses Energybending to strip Ozai of his Firebending powers, ending his ability to wage war. Afterwards, Aang raises and lowers nearby water to undo the damages that the Fire Nation caused.

The Order of the White Lotus liberates Ba Sing Se in the name of the Earth King. During his coronation, Zuko promises to aid the world in the postwar reconstruction. Sometime after the ceremony, Zuko visits Ozai's prison and demands he tell him the location of the banished Ursa, Zuko's mother. A final scene depicts the main cast gathered in Iroh's new tea shop, the Jasmine Dragon. Aang and Katara kiss passionately upon the shop balcony as the series ends.