Tokugawa Ieshige
Matsudaira Sadanobu was the seventh son of Tokugawa Munetake, of the Tayasu branch of the Tokugawa clan. The Tayasu was one of the "gosankyō", the senior-most of the lesser cadet branches of the Shōgun's family, and was thus the grandson of the reform-minded eighth shōgun Tokugawa Yoshimune. The Tayasu house stood apart from the other cadet branches resident in Edo Castle, living a more austere lifestyle, following the example set by Yoshimune—in Munetake's words, the praise of manly spirit ("masuraoburi") as opposed to feminine spirit ("taoyameburi"). It also set itself apart from the other branches due to its history of thwarted political ambition—the founder, Munetake, had hoped to become his father's heir but was passed over for Yoshimune's eldest son, Tokugawa Ieshige. As a result, Sadanobu was brought up from a very young age with the hopes of being placed as the next shogunal heir, despite his poor health as a child. His education was very thorough, being done along Confucian lines, and by his teens Sadanobu had already read and memorized much of the Confucian canon. As he matured, there was a further onus on Sadanobu for success as several members of the Tayasu house began to die young. Further attempts were made by the family to place Sadanobu as the next shogunal heir, but they were thwarted by the political clique of Tanuma Okitsugu, who was then in power as the chief "rōjū".