Ozai

"You're weak, just like the rest of your people! They did not deserve to exist in this world — in my world! Prepare to join them. Prepare to 'die!"

- Ozai to Avatar Aang

Fire Lord Ozai is the main villain in the cartoon series Avatar: The Last Airbender, though he doesn't show his face until the beginning of season 3.

Origin
Ozai was born to Fire Lord Azulon, as the younger brother to Fire Prince Iroh, who was favored by their father and who would inherit the throne. He married a noblewomen named Ursa, who bore him two children, Prince Zuko, the eldest who was favored by Ursa, and Princess Azula, who Ozai would favor and who would become a prodigy in the art of Firebending.

When his nephew, Lu Ten, was killed in battle he asked his father, Azulon to relinquish the title of Firelord to him. Outraged by this request, Azulon ordered Ozai to kill his son, Zuko. At first, Ozai was willing to comply with this request, however, his wife, Ursa managed to save her son's life by taking his place. However, instead of being killed, she was banished. Azulon mysteriously died at about the same time (indicating that Ursa possibly killed him), and at his funeral Ozai was crowned Fire Lord, as Iroh was too sad to accept the role as leader of the Fire Nation.

Later in life, when Zuko was thirteen years old, he attended a military meeting, where one of Ozai's generals suggested that they send a group of soldiers to distract the troops of the Earth Kingdom while they had their other soldiers ambush the Earth army and then overcome the capital of the Earth Kingdom, Ba Sing Se. Outraged, Zuko spoke out against this plan, and he was punished severely: being forced into an Agni Kai against his own father. Zuko was unwilling to hurt his father, and as a result, the Fire Lord blasted his son, creating a huge scar on his face. Ozai banished Zuko unless he found the Avatar, master of the four elements.

Goals and Ambitions
Ozai's main goal is to conquer all the nations and rule over them under the title of "The Phoenix King". To do this, he attempted to use Sozin's comet to wipe out any remaining forces that opposed him.

Role in the Series
Ozai is mentioned several times throughout the show, but rarely appears. He is first mentioned by name in the episode "King of Omashu", by King Bumi. Most of his appearances are in visions that Aang has or in flashbacks of Zuko's past. The first time we see him outside of flashbacks of visions is in the finale of the first season, where he gives his daughter Azula the orders to capture his son and brother, who he blames for the failure in the invasion of the Northern Water Tribe. However, in all of his appearances prior to season 3, his face is covered by shadows.

He appears far more in the very last season of the show, where his face is shown for the first time when he welcomes his son Zuko back home after he helped Azula and the Dai Li "kill" the Avatar (he survived thanks to some mystical healing water) and conquer Ba Sing Se. Throughout the first half of the season, Aang's gang and Zuko see many paintings and statues of him.

The night before the Avatar and his allies invade the capital of the Fire Nation, where the solar eclipse will stop any firebending, the Fire Lord holds a war meeting with his children and his general. At this meeting, he came up with the plan to use his newly built airships to commit genocide against the people of the Earth Kingdom, leaving only the Fire Nation and the massively divided people of the Water Tribe left on the planet.

During the invasion, Ozai and many other nobles and soldiers hid in a giant metal underground dome near the capital city. Zuko confronted his father during the eclipse, informing him of his choice to join the Avatar, teach him Firebending and free the Fire Nation from Ozai's tyranny. When he is about to leave, Ozai tricks him into staying by telling him the story of his mothers death, revealing she may still be alive. When he finishes the story, the eclipse ends and he shoots lightning at Zuko, who redirects it and escapes.

His next appearance is around three days before Sozin's Comet arrives, which will increase the powers of any firebender to an extreme degree. He appoints Azula as the new Firelord, as he will be known as the Phoenix King, who will rule over all the nations and it's leaders.

On the day of the comet's arrival, he boards the largest of the Fire Nations fleet of airships and heads towards the Earth Kingdom. While some of the Avatar's comrades take control of an airship and sabotage the rest of the fleet, Avatar Aang, having learned how to use all four elements, destroys the engine of Ozai's flagship and they begin to duel. For most of the fight, Aang and the Firelord are equally matched, with AAng using his skill in the art of bending each element to block most if not all of Ozai's blows.

Eventually, Ozai starts to bend lightning, but it backfires when Aang begins to redirect it at Ozai. However, unwilling to kill another human being, he willingly misses the Phoenix King, who begins to overpower the Avatar, forcing him to entrap himself in a boulder. However, after many strong blows, Ozai shatters the rock and sends Aang flying. However, the scar on his back where Azula killed him with lightning is hit, causing him to go into the Avatar State, where he has the power and knowledge of all the past avatars. He proceeds to outclass Ozai in every way, and finally pins him down, and prepares to deliver the final blow, but Aang is still unwilling to take a life and closes the Avatar State and releases Ozai.

Ozai calls him a fool and attacks him from behind, but Aang traps him again and uses forgotten art called "Energybending" to take away Ozai's bending powers. During the battle, the Avatar's allies, defeated Azula, retook Ba Sing Se and destroyed the Fire Nation's fleet. Completely defeated, powerless and broken, Zuko, as the new Fire Lord, throws Ozai into prison and interrogates Ozai on the whereabouts of his mother.