Aizen Sosuke

Sōsuke Aizen
Bleach character
Sōsuke Aizen by Tite Kubo
First appearance	Bleach manga chapter 79 Bleach anime episode 23
Created by	Tite Kubo
Voiced by	Japanese Shō Hayami English Kyle Hebert
Profile
Species	Soul Reaper

Sōsuke Aizen (藍染 惣右介, Aizen Sōsuke) is a fictional character and the main antagonist for most of the first half of the manga series Bleach (and the most significant one for the entirety of the anime adaptation) created by Tite Kubo. He is the captain of the Fifth Division when he is first introduced, but later betrays the Soul Society and becomes the series' main antagonist, before Ichigo Kurosaki and Kisuke Urahara defeat him. His former lieutenant is Momo Hinamori.

Aizen spent much of his career in the 5th Division, eventually becoming its lieutenant under the former captain, Shinji Hirako. Aizen also gained followers in Gin Ichimaru and Kaname Tōsen. A century before the series' setting, after Kisuke Urahara created the Hōgyoku, an item that he believed creates Soul Reaper/Hollow hybrids, Aizen began to experiment using the Soul Reapers that became the Vizards. Among his test subjects was Shinji, who knew Aizen was up to no good but learned too late that Aizen used his mistrust against him. Having also framed Kisuke for the Vizards' creation and forced his exile, Aizen learned the Hōgyoku actually grants its user's desires if they have the will to carry it out. But as Kisuke took the Hōgyoku with him, Aizen bides his time to take the item when the time comes.

At some point, Aizen saw the potential of Shuhei Hisagi, Momo Hinamori, Izuru Kira and Renji Abarai, and Aizen took the latter three into his division, while sending Shuhei to the 9th division under Tōsen. While Kira and Hinamori were obedient and loyal, becoming the lieutenants of the 3rd and 5th Divisions under Gin and Aizen, respectively, Renji proved to be too rebellious and was transferred to the 11th Division (and later to the 6th, where he too became a lieutenant). Aizen also continued his experiments on Soul Reaper/Hollow hybrids with his creations Metastacia and White playing a respective role in the life of Rukia Kuchiki and those of Isshin Shiba and Masaki Kurosaki. In the case of Isshin and Masaki, Aizen knew of Ichigo's existence that resulted from White's actions and considered the youth a being worth studying to the point of engineering the hardships he would face later in life.