松平定信
was a Japanese "daimyō" of the Bakumatsu period, who was the last ruler of the Kuwana Domain. Sadaaki was the adopted heir of Matsudaira Sadamichi, the descendant of Sadatsuna, the third son of Hisamatsu Sadakatsu (1569–1623), who was Tokugawa Ieyasu's brother. His family was known as the Hisamatsu Matsudaira clan. It was to this family that Matsudaira Sadanobu also belonged.