Sousuke Aizen is a central antagonist in the anime series Bleach. Initially introduced as the kind and gentle captain of the 5th Division in the Gotei 13, Aizen's true nature is revealed as a cunning and manipulative villain with immense power and intelligence. He orchestrates a complex plan to overthrow the Soul Society and become a god-like being. Aizen's calm demeanor and strategic mind make him a formidable adversary, and his betrayal shocks the other characters. His role in the series highlights themes of power, betrayal, and ambition.