Background
Because he was a son of Tokugawa Ieyasu, he is often referred to, retroactively, as Tokugawa Nobuyasu (徳川 信康).
松平 信康
Because he was a son of Tokugawa Ieyasu, he is often referred to, retroactively, as Tokugawa Nobuyasu (徳川 信康).
His tsūshō ("common name") was Jirōsaburō (次郎三郎). He was called also "Okazaki Saburō" (岡崎 三郎), because he had become the lord of Okazaki Castle (岡崎城) in 1570. Nobuyasu was Ieyasu"s first son.
As a child Nobuyasu was sent to the Imagawa capital of Sunpu, located in Suruga Province (modern-day Shizuoka Prefecture) as a hostage.
Later he was named keeper of Okazaki Castle in Mikawa Province (modern-day Aichi Prefecture), the birthplace of his father, and took part in the Battle of Nagashino in 1575. Nobuyasu is not believed to have been a popular figure in his time, as his demise might attest.
(In particular, supposedly Sakai Tadatsugu"s own personal disregard for Nobuyasu led him to not refute the suspicion) Despite this, it is said that Tokugawa Ieyasu deeply regretted the part he played in his son"s death.