|Previous Affiliation||Arrancar Army, Gotei 13, Soul Society, 5th Division|
|Previous Occupation||Leader of the Arrancar Army, Captain of the 5th Division, Lieutenant of the 5th Division, Instructor at the Shin'ō Academy|
|Previous Team||5th Division|
|Previous Partner||Gin Ichimaru, Kaname Tōsen, Shinji Hirako, Momo Hinamori|
|Base of Operations||Las Noches, Hueco Mundo|
|Bankai||Net Yet Revealed|
AppearancePrior to his Defection from the Soul Society, he appeared as a mild-featured man with brown scholarly hair enhanced by square glasses. He wore the Standard Shihakushō with a Captain's Haori. However, During his ascention to Hueco Mundo, he removed his glasses and Swept his hand through his hair, revealing menacing eyes and a very different hairstyle; his hair is now swept back, with a Strand hanging in his face. As he had Previously Revealed to Renji Abarai, the "Sōsuke Aizen" that they all knew never existed to begin with and this would Seem to be a Visual Representation of that Claim.
In Hueco Mundo, Aizen is first Seen wearing Arrancar clothing Over his Shihakushō. Afterwards, after Orihime Inoue is taken to Las Noches, Aizen wore full Clothing Similar in Style to the Arrancars.
When fighting Kisuke Urahara, Yoruichi Shihōin and Isshin Kurosaki and eventually fighting Ichigo Kurosaki for the final time, the Hōgyoku gives him a Variety of Transformation Changes Since he has the Hōgyoku Implanted inside his Chest.
Aizen's Appearance Changes again upon his Initial Defeat by Ichigo Kurosaki. Aizen loses all of the Physical Changes Made by his transformations from the Hōgyoku and returns to the Physical form he had Prior to transforming.
Aizen Initially appeared to be a very kind, well-respected Captain and was looked up to by many, especially his Lieutenant Momo Hinamori. However, this was just a Mask to Disguise his Manipulative and Very Dangerous Nature. In truth, he cares very little for his underlings (both Past and Present), and is willing to use almost everyone around him as Pawns to achieve his means. In his own words, Aizen Claims to be Unaffected by any form of morals or ethics, as he views them as mere Restrictions on his Potential. He is, therefore, willing to stop at nothing to further his selfish ambitions, including Manipulating or Killing anyone if he Deems it to be necessary. He is fond of long, Complicated, and Somewhat Convoluted plots, and frequently appears to toy with his underlings for amusement. Unlike most of the Other Shinigami who appear to have Some kind of honor and kindness, including some Espada, Aizen lacks genuine Compassion and honor.
Despite his Current Villainous Status and former Position of authority, Aizen is a Surprisingly Polite, Soft-spoken intellectual, often addressing his Subordinates by their given names. He rarely shows any sign of alarm or distress and often has entire Situations Planned out well in advance. Whenever Confronted, Aizen is Casual and Uncaring, attempting to draw out a Conversation and make small talk, which often Infuriates and Provokes those he is talking to.
In his free time, he Often read and he also gave a Special lecture of Calligraphy at the Shin'ō Academy, given that he excelled in this Branch of arts. This Optional Course was Immensely Popular among the Shinigami Students, and many of them felt great Sorrow at Aizen's Sudden Departure.
As the Commander of his army of Arrancar, Aizen Controls his minions either through acquired respect or fear. Ulquiorra Cifer, one of his noticeably loyal Subordinates, revealed in a Conversation with Orihime Inoue that they are all there to further Aizen's ambitions. For more rowdy Individuals like Grimmjow Jaegerjaquez, he keeps them in line through Intimidation and mind games. The Arrancar Aisslinger Wernarr also claims that they follow Aizen Because he has no fear, Something which beings born from fear and despair find Inspiring. Other Arrancar Occasionally follow Aizen for reasons unique to themselves, such as Szayelaporro Granz, who follows Aizen with the hopes that he will eradicate the world of all non-Hollows.
To date, the equally manipulative Gin Ichimaru is the Only Person who Seems to be able to see through Aizen's Manipulation. Ichimaru has also shown that he has some sense of Aizen's emotions and feelings, Correctly Identifying that Aizen was enjoying the Invasion of Ichigo and his friends and their Successes within Las Noches, as well as Picking-up on the fact that Aizen had registered the arrival of Hinamori in the Battle of Fake Karakura Town and was surprised by it. By contrast, Kaname Tōsen has shown no Such Understanding and has fallen victim to one of Aizen's more minor mind games when Aizen off-handedly manipulated him into punishing Grimmjow for him while Aizen himself Kept up his appearance of Benevolence.
Aizen's true Objective was to Overthrow the King of the Soul Society. As he and his fellow traitor Captains were Departing from the Soul Society, he told Jushiro Ukitake that "no one has Stood on the top of the world", not even the gods, but he aspires to "stand on the heavens and end the Unbearable Vacancy on the world's throne". To do this, he needs the Oken (王鍵, Royal Key), a tri-pronged golden key that opens a portal to the dimension in which the Spirit King resides. While the location of the key is known only to Captain-Commander Yamamoto, Aizen knows how the Original One was Created and how to Manufacture another. To do this, 100,000 Souls need to be gathered together (which will kill all the entities used) and vaporize a significant Portion of the area used in its forging. His sights are therefore set on Karakura Town, which has an Unusually large Concentration of Spirit Particles.
According to Kisuke Urahara, Since Mastering the Hōgyoku, Aizen has become less cautious in battle; noting that before he subdued the device Aizen would not have allowed him to use level 90 Kidō; Aizen admits that his new powers allow him to let his guard down. Also due to this newfound power, he has developed more of a Seemingly arrogant and Overconfident attitude, often not even thinking his attacks or defense through any longer like he used to, or even Bothering to find out the effects of his Opponents' and his own attacks. In his newest form, he has also Developed a Severe Superiority Complex, Believing he is now above both Shinigami and Hollows, a transcentant being. Because of his Superior attitude and high Intellect, Aizen is easily enraged when facing Something or Someone that he doesn't Understand; for example, when Witnessing Ichigo in his "Final" form, Aizen Becomes furious Because he is Unable to Comprehend how a Human has surpassed him so Much.
HistoryAt an Unknown Point in the Past, Aizen Became apart of 5th Division Under Captain Shinji Hirako. He Invested himself in the research and Creation of the Hōgyoku even Before Kisuke Urahara did. To this end, he Sacrificed Hundreds of Shinigami and Hundreds of Rukongai Citizens who bore Shinigami talents to his own Hōgyoku. But it was not Satisfied with this. He is then Seen Standing in a Clearing with three Other Shinigami who are Kneeling Before him by Gin Ichimaru. One of the Shinigami hands Aizen the Hōgyoku. Aizen then Puts it in a glass and then hands it back to the Shinigami. Aizen and his Subordinates leave an Unconscious Rangiku Matsumoto a Short Distance away. Aizen eventually Caught his Captain's attention, and was Promoted to a lieutenant in Order for Shinji to watch over him Closely. However, this Shinji's act only helped the Realization of his Plans.
110 years ago Aizen was Seen making his way to the 5th Division living quarters of his Captain. He and Shinji had a Discussion about Style and trends Before they made their way to the Promotion Ceremony being held at the 1st Division headquarters. As they got there, Aizen witnessed Hiyori Sarugaki attack his Captain and the two got into a Childish argument. He followed behind while the Other Captains Congregated and had a brief discussion on the Status of the Gotei 13. Overhearing Shunsui Kyōraku Mention that the Previous Captain of the 12th Division was Promoted, Aizen Interrupted and asked what Kyōraku Meant by it. Aizen Initially Conjectured that the Promotion was to Central 46. However, Shunsui explained that it had nothing to do with the Central 46 and that the Previous Squad Captain Kirio Hikifune had been accepted into the Zero Division also known as the Royal Guard. Aizen was left Surprised at the Revelation.