Fire Lord Ozai is the tyrannical leader of the Fire Nation. He is the father of Zuko and Azula. He banished his son for speaking out of turn in a war planning session, with the condition that he may return if the Avatar was captured.
Fire Lord Ozai is the only known Fire Lord in the film. Being raised a coldhearted person, he neglected his son Zuko yet openly showed much love for his evil daughter, Azula. Not much is known of Ozai's past. After his son Zuko had spoken out of turn to a general in defense of some of his friends who were going to sacrificed in battle, Ozai sentenced his son to an Agni kī Duel (अग्नि की डूएल - "Duel of Fire"). When Zuko showed up, it was Ozai himself he was to fight, but Zuko would not fight his father. Ozai mocked him, "I should bring your sister up here to beat you" then burned his son to teach him a lesson. He then banished Zuko, leaving the former GeneralIroh to take care of him from then on.
Ozai was also close allies with Zhao and had common goals, including capturing the Avatar before his son Zuko, which would effectively end his banishment. He also shared roles with him in the discovery of the hidden library and information therein that can be used to eliminate the Ocean and Moon Spirit. After acknowledging their destiny to have found this information he ordered Zhao to eliminate the spirits, take the Northern Water Tribe City, and destroy the Avatar at the same time. After Zhao died during the Siege of the North, his daughter Azula gladly accepted the task he requested of her to stop the Avatar from mastering earth and fire, and give the Fire Nation time for Sozin's Comet to arrive. His main enemy is the Avatar.
Ozai is played by New Zealander Cliff Curtis. Curtis said that "I'm kind of like the Darth Vader character for that franchise", which is interesting because in the original Star Wars trilogy, Darth Vader was shown as the main antagonist like animated Zhao, while the Emperor was hidden like animated Ozai. He also said that "I haven't watched the TV series to get confused by it." Referring to Shyamalan, "I wanted to take his lead on what way he wanted to take the franchise. He's had to condense, I don't know how many episodes, but two or three years' worth of television episodes into three movies."
The character in the film is the main antagonist of the film series, much like the animated Zhao is in the original series. Along with roles originally played by the animated Ozai, he played many roles of the animated Zhao. In some cases, the roles are jointly shared with the film Zhao, particularly the plan to eliminate the Ocean and Moon Spirits in the Siege of the North. The characterization for the animated Zhao is more closely depicted with this Ozai than with the film Zhao, e.g., sinister and devious, rather than cocky and ambitious.
Ozai is not hidden in the movie like in the show, instead he is seen clearly at the beginning of the film.
Ozai also does not have long hair or a beard as he did in the show, but instead has a simple crew cut. However, a family portrait (the one held by Zuko before his firebending training) implied that he did have long hair and a beard when he was younger, only to shave it off after he took over as Fire Lord from Azulon. His sideburns are more prominent than the film Zhao, which animated Ozai also did not have.
In the animated show, the library was found by Zhao years before the siege, when he was a junior Lieutenant serving under General Shu in the Earth Kingdom. In the movie, it was found months before the siege by the younger film Zhao, who presented his findings to this film Ozai.
While the animated Zhao considered the elimination of the Ocean and Moon Spirits as his destiny, this Ozai considered it as a shared destiny with the film Zhao: "It is destiny that we have found this information, Zhao".
During the Siege of the North in the film, Zhao told Iroh not to worry about the Moon Sprit's power because "Your brother, Fire Lord Ozai, and I have decided it's in our best interest to kill the Moon Spirit." This may be a nod to the animated Zhao character being split, as it may be more accurate to say "Fire Lord Ozai ordered me to kill the Moon Spirit."
In the series, Ozai wears a simple red, burgundy, and gold robe, yet in the film, Ozai wears a very fancy crimson colored robe with a gold, red, and black chestplate and a long black and gold cape. Cliff Curtis said in an interview that the costume was "sort of like a cross between Roman and kind of Greek, [a] gold, Roman and Greek military/samurai military [uniform]."
This film Ozai was very much involved in military affairs, with Naval Commanders and Army Generals reporting directly to him, bypassing the need for Naval Admirals or Army Marshals. As such, the Fire Nation may be under a military dictatorship, much like the Roman Empire under Julius Caesar.
In the movie novelization, after Zhao accused Zuko to be Blue Spirit (albeit without proof), Ozai ordered Zhao to "take care of this" for him and "make appear to be an accident. An unfortunate accident." This was changed in the actual movie: Zhao sabotaged Zuko's ship despite being ordered to leave him in his isolation, making Ozai seem less cruel. Voice-overs of Ozai inquiring any news of his son from Zhao was also added.
Ozai is an interesting composite of his animated counterpart and the animated Zhao, the latter being decomposed into separate two film characters: one merged with this film Ozai (played by Cliff Curtis) and the other as a younger film Zhao (played by Aasif Mandvi) serving as an "extension" to this older self and apparently also his illegitimate son, turning the relationship dynamics between "Zhao Jr." and Zuko similar to Edmund and Edgar in King Lear. As such, the film contains many scenes between him and Commander Zhao, a relationship not illustrated in the cartoon.