Aizen has short, brown hair that is slicked back, with one lock hanging down in front.Before his deflection from the Soul Society, Aizen's hair hung down and he wore glasses and a Captain's haori.
During the Soul Society arc, Aizen seemed to be something of a benevolent father figure. After he revealed his deception, he showed a much more psychopathic side of himself. Aizen became much more power-hungry, and he displayed no qualms about killing anyone, even his own subordinates, just to gain a momentary advantage. He was also supremely arrogant, declaring that he would let the majority of the Gotei 13 live to witness his greatness, but slay Head Captain Yamamoto because he was "Soul Society's history." He has always, however, been extremely intelligent.
Soul Society ArcEdit
After Rukia Kuchiki is brought back to Soul Society, Aizen proceeded with a conspiracy to take over Soul Society. He murdered the Central 46 and began masquerading as them from within their housing quarters. Shortly after a Captains Meeting was called to discuss the Ryoka Invasion, he accused Gin Ichimaru of being up to something, which was actually a staged encounter to make Toshiro Hitsugaya suspicious of Gin.
At an undisclosed point in the past, Aizen used his Zanpakuto's powers to put all of the Captains and Lieutenants under hypnosis. The day after the Captains Meeting, he would use this to make them think that he had been murdered. He convinced his Lieutenant, Momo Hinamori, through a pre-death letter, that Hitsugaya was behind a plot to destroy Soul Society, and was probably Aizen's killer. Rukia's execution date was moved up, yet again, by Aizen.
Gin Ichimaru later leads Momo to the Cebtral 46 chamber, where she was greeted by Aizen, who was very much alive. Momo was overjoyed, but Aizen stabbed her in the stomach, revealing himself to be the one behind the conspiracy. As he was about to leave, Hitsugaya attempted to stop him, but was easily defeated. Aizen was then stopped, yet again, by the Fourth Squad's Captain Unohana, and her Lieutenant Isane Kotetsu, who had worked out that he faked his death and was likely orchestrating a coup. Aizen explained his plan along with perfect hypnosis and the revelation that Gin Ichimaru and Kaname Tosen were also part of the conspiracy, and left with Gin to Sokyoku Hill, where he found Rukia in Renji's arms.
Renji refused to hand Rukia over and drew his sword to fight Aizen, but he easily destroyed Renji's shikai. Aizen prepared to attack Renji, but was stopped when Ichigo showed up and parried his attack. Ichigo and Renji team up, but were no match for Aizen. He wounded Renji, Ichigo, and seventh Squad Captain Komamura, who showed up to confront him and Kaname.
Aizen explained to a barely conscious Ichigo that a device called the Hogyoku was hidden inside Rukia by Kisuke Urahara, explained at this time as being able to cause Shinigamification and Hollowfication. Aizen states that he wanted Rukia killed in order to enhance his powers with the Hogyoku. However, Aizen had scoured Urahara's files for another method to extract it, in the event that his plan failed. Using that device, he removed the Hogyoku from Rukia's body and ordered Gin to kill Rukia, but Byakuya intervened, taking the attack for her.
Aizen prepared to finish Byakuya off and leave, but was stopped by Yoruichi and Soi Fon, who threatened him with decapitation. Soon, the entire Soul Society showed up on Sokyoku Hill, aided by Jidanbo and Kukaku Shiba. However, this did not stop Aizen, a number of Menos Grandes tore open the sky to take him, Tosen, and Gin away to Hueco Mundo. As he left, Aizen shattered his glasses and smoothed his hair back, announcing that he would one day "stand on top of the world."