was a Japanese daimyo

Daimyo

is a generic term referring to the powerful territorial lords in pre-modern Japan who ruled most of the country from their vast, hereditary land holdings...

 of the late Sengoku period

Sengoku period

The or Warring States period in Japanese history was a time of social upheaval, political intrigue, and nearly constant military conflict that lasted roughly from the middle of the 15th century to the beginning of the 17th century. The name "Sengoku" was adopted by Japanese historians in reference...

 through early Edo period

Edo period

The , or , is a division of Japanese history which was ruled by the shoguns of the Tokugawa family, running from 1603 to 1868. The political entity of this period was the Tokugawa shogunate....

, who served the Tokugawa clan

Tokugawa clan

The was a powerful daimyo family of Japan. They nominally descended from Emperor Seiwa and were a branch of the Minamoto clan by the Nitta clan. However, the early history of this clan remains a mystery.-History:...

. As one of the Tokugawa family's foremost military commanders, he was considered one of its "Four Guardian Kings"

Shitenno (Tokugawa clan)

The is a Japanese sobriquet describing four highly effective samurai generals who fought on behalf of Tokugawa Ieyasu in Sengoku period. They were famous during their lifetimes as the four most fiercely loyal vassals of the Tokugawa clan in the early Edo period....

 (shitennō 四天王). His court title was Shikibu-dayū (式部大輔).
Sakakibara Yasumasa was born in Tenmon 17 (1548), the 2nd son of Sakakibara Nagamasa, in the Ueno district of Mikawa Province

Mikawa Province

is an old province in the area that today forms the eastern half of Aichi Prefecture. It was sometimes called . Mikawa bordered on Owari, Mino, Shinano, and Tōtōmi Provinces....

. The Sakakibara were hereditary retainers of the Matsudaira (later Tokugawa) clan, being classified as fudai

Fudai

was a class of daimyo who were hereditary vassals of the Tokugawa in Edo period Japan. It was primarily the fudai who filled the ranks of the Tokugawa administration.-Origins:...

.