Japanese military leader who helped both Toyotomi Hideyoshi and Tokugawa Ieyasu in their attempts to unify Japan. As an ardent Buddhist, he also led the struggle to ban Christianity from Japan.

A relative of Hideyoshi, Katō entered his service upon reaching manhood and soon distinguished himself in battle. When Hideyoshi invaded Korea in 1592, Katō spearheaded the campaign and fought so ferociously that the Koreans nicknamed him “Devil Kiyomasa.” Upon Hideyoshi's death in 1598, Katō returned to Japan and aided Ieyasu, who as chief regent to Hideyoshi's young son was attempting to maintain his position against a coalition of feudal lords.

For his services Katō was made the hereditary lord of the large Kumamoto fief in southeastern Japan. In Kumamoto he was noted for the effort he put into his riparian projects and the construction of his castle. Upon his death his fief was transferred to the Hosokawa family by the Tokugawa.