Sōsuke Aizen (藍染 惣右介, Aizen Sōsuke) is the former captain of the 5th Division of the Gotei 13, whose lieutenant was Momo Hinamori; before his captaincy, Aizen served as the division's lieutenant under Shinji Hirako. For over a century, Aizen masqueraded as a benevolent Shinigami officer while secretly plotting his betrayal and conducting depraved experiments, which around 100 years ago led to the Hollowfication of the Visored and their (alongside Kisuke Urahara's) forced exile.