As a young prince, Sozin was best friends with Avatar Roku. After Sozin took up the throne and Roku became a fully realized Avatar, their friendship became strained to the breaking point as Sozin desired the Fire Nation to encompass the world, a plan to which Roku was strongly opposed. Following a confrontation over this which ended in Sozin's defeat, neither spoke to the other until they were both very old. Sozin betrayed his old friend to his death and began waging war. Using the fire-enhancing power of a comet, Sozin eradicated the Air Nomads to try to eliminate the next Avatar, but failed. He spent the last years of his life hunting the new Avatar in vain.
As a young prince, Sozin was best friends with Avatar Roku. After Sozin took up the throne and Roku became a fully realized Avatar, their friendship became strained to the breaking point as Sozin desired the Fire Nation to encompass the world, a plan to which Roku was strongly opposed. Following a confrontation over this which ended in Sozin's defeat, neither spoke to the other until they were both very old. Sozin betrayed his old friend to his death and began waging war. Fire Lord Sozin was the instigator of the War and the Fire Lord before his son, Azulon. He was grandfather to Iroh and Ozai and great-grandfather to Zuko, Azula, and Lu Ten.
Using the fire-enhancing power of a comet, Sozin eradicated the Air Nomads to try to eliminate the next Avatar, but failed. He spent the last years of his life hunting the new Avatar in vain. Shortly before his death, he regreted all he done.
YouthRoku and Sozin at their birthday celebration.In his youth, Prince Sozin and Avatar Roku were best friends and even shared the same birthday, which they celebrated together. It could be said that both of them were also firebending masters at an early age, given that Roku was the Avatar, which was then unknown, and Sozin's family had a natural affinity for their element. At their sixteenth birthday celebration, Roku was told by the Fire Sages that he was the Avatar, and the two friends were forced to separate as Roku goes to learn mastery of the three other elements. Before leaving, Sozin came by to talk and was told by Roku that the sages told him to bring nothing, as the Avatar needed no material goods. By this statement, Sozin gave him a gift: the headpiece worn by the Crown Prince of the Fire Nation, hoping that he was at least allowed to have that.
Treason12 years later, Roku returned to the Fire Nation and Sozin had become Fire Lord. At Roku's wedding, Sozin took the position of his best man. At the wedding, Sozin commented that the Fire Nation was going through a period of great prosperity and told Roku that together, the two of them could spread it to the world by expanding the empire. Roku is greatly disturbed by this, telling Sozin that the four nations are meant to be kept separate and that he should not think of this again. Sozin leaving Roku to die. Several years later, however, Roku discovered that Sozin had set up colonies in the Earth Kingdom and came to rebuke him, leading Sozin to attack him. The two engage in a battle, with Roku finally destroying most of the palace and defeating Sozin. Roku spared his life because of their past friendship but warned him never to move forward with his plans again, or it would result in his "permanent end."
25 years later, Roku's home island was consumed in a volcanic eruption so massive that Sozin could see and feel it from a hundred miles away. The Fire Lord flew in on his dragon to assist his old friend. The two used their bending to try to contain the lava flow but were hindered by poisonous gases, which eventually overwhelmed Roku, leaving him lying on the ground and begging for his old friend's help. Sozin suddenly realized, however, that Roku's death would allow him to fulfill his plans, and left his old friend to die along with his dragon, Fang.
Invasion12 years after Roku had died, Sozin used the power of a comet to enhance the power of his firebender army and launched a genocidal attack on the Air Nomads in an attempt to kill Aang, the new Avatar, and halt the Avatar cycle. However, Sozin failed, as Aang had ran away from the Air Nomads some time before. Sozin spent the rest of his life searching, so that he could find and destroy the last airbender.
After the comet, he lived 20 more years and had a son, Prince Azulon. It is unknown what kind of relationship Sozin had with his son, but Azulon would come to share his thirst for world domination, and became a terrifying dictator. It is unknown who Sozin's wife was.
One of his lesser-known military accomplishments during this period was the Battle of Han Tui, which was applauded as a magnificent display of skill and military cunning.
At some point during his reign, probably after Roku's death, Sozin started the tradition of hunting dragons for glory. For a firebender to be able to kill a dragon, the original firebenders, he would be showered with glory and praise, and earn the honorary title "Dragon". This lead to the dragons' near-extinction.
However, it appeared that at the end of his life he regrets what he started by stating "As I feel my own life dimming, I can't help but think of a time when everything was so much brighter....".
He eventually died at age of 102. Rumors from citizens suspect he lived to be older due to the influence of the power of the comet. According to what was learned in Fire Nation schools, Sozin died peacefully in his sleep, a very old and successful man.
The War that Sozin began finally ended in 100 ASC when Avatar Aang reemerged after a hundred years of suspended animation and defeated Sozin's grandson, Fire Lord Ozai.
Sozin removing the magma's heat.Being Fire Lord, Sozin was a powerful firebending master. When he was young, he sparred with Avatar Roku and defeated him on at least one occasion. When Roku confronted him years later about his actions in the Earth Kingdom, Sozin attacked him by unleashing a massive wave of fire against him, one of the most powerful blasts in the series, even though he did not have access to the power Sozin's Comet provided. However, he was still no match for Roku, who had the other three elements and the Avatar State at his command. When he helps Roku tame an erupting volcano, he uses a technique to redirect heat, cooling the lava. The technique he used appears to be similar to Iroh's lightning redirection move.
Sozin was a very knowledgeable strategist. When he and Roku were teenagers, Sozin tricked Roku into tripping over a tree root in order to win a sparring match. Sozin's knowledge made him a capable military leader. During the War, Sozin won the Battle of Han Tui by taking advantage of the fact that the enemy had been in the middle of a drought and downwind. According to Azula in a later recounting of the event, their defenses burned to a crisp in minutes.
- Main article: Fire Nation Royal Family Tree
- Azulon (son)
- Ilah (daughter-in-law)
- Iroh (eldest grandson)
- Lu Ten (eldest great-grandson)
- Ozai (youngest grandson)
- Ursa (granddaughter-in-law)
- Zuko (youngest great-grandson)
- Azula (youngest great-granddaughter)
- Sozin's name, (蘇進, pintin: sū jìn), translates as "revival and progress".
- Sozin's name is closely related to the Persian name "Souzan", which means "fire".
- Sozin's name is spelled very similar to Yamana Sōzen's surname. Both had disputes with another person, Sozin with Roku and Yamana with Hosokawa Katsumoto, which assisted in the creation of a war for both, although unlike Yamana and Hosokawa, Sozin and Roku were never actually at war against each other.
- Fire Lord Sozin had his son, Fire Lord Azulon, very late in life; since Azulon was born shortly after the start of the war, Sozin would have been 82 years old at the time.
- It is also possible that Sozin's father was mentioned once in "The Avatar and the Fire Lord", he was an elderly man when he had Sozin. This is slightly hinted when the Fire Sages arrived to announce Roku as the Avatar, Sozin worriedly asked about his father's health - a further hint is Sozin's ascendancy only a few years later, when Roku returned.
- Sozin's official portrait features firebending soldiers, a scroll in his hand, and a comet, signifying his military buildup and the beginning of the War, the many reforms under his rule, and of course, the coming of the comet which now bears his name.
- Sozin appeared to have made the biggest impact of any character on the world, single-handedly starting the War, and then ordering that all of the Air Nomads be hunted down.
- According to "Avatar Extras" an early script of the premiere episode included a friendly duel between Avatar Roku and Sozin when they were younger, similar to the one shown in "The Avatar and the Fire Lord".
- Avatar Extras state that people in the Avatar universe believe that the power granted from Sozin's comet is what allowed Sozin to live as long as he did.
- It is unknown how he knew that the Avatar wasn't in any of the air temples that he destroyed.
- Sozin was the only known political figure to force an Avatar to choose between loyalty and duty and get away with it, albeit being threatened and having to wait until Roku died.
- Sozin was also the Fire Lord responsible for manipulating firebending's roots, changing it to match his militaristic and conquering goals.
- Sozin began the tradition of hunting dragons, the original firebenders. This likely helped reduce the spirituality of the nation to the point where the Fire Sages would be more inclined to obey him, and further reduced the old understanding of firebending i.e. the importance of the dragons and the sun.
- Sozin is the earliest Fire Lord developed in the series. He is also the oldest Fire Lord on record.