Sōsuke Aizen (藍染 惣右介, Aizen Sōsuke) is the former captain of the 5th Division in the Gotei 13. He later leaves Soul Society with his followers, Gin Ichimaru and Kaname Tōsen. His lieutenant was Momo Hinamori. He formerly served as the lieutenant of the 5th Division under Shinji Hirako. After waging war against Soul Society with an army of Arrancar, Aizen was defeated by Ichigo Kurosaki and sealed away by Kisuke Urahara, and then imprisoned for his crimes.