Born to the Sakakibara of Mikawa Ueno. Childhood name Koheita. Young he served Matsudaira Motoyasu (later Tokugawa Ieyasu) and won early merit in the Mikawa Ikko uprising and elsewhere.
When Imagawa Yoshimoto fell at Okehazama, Yasumasa was a young warrior backing Ieyasu's independence. In the war free of Imagawa he gained further experience.
In Ieyasu's unification of Mikawa he showed bravery against any foe. With colleagues Honda Tadakatsu and Ii Naomasa he laid the base for later fame as one of the Four Heavenly Kings.
He fought at Anegawa and backed Ieyasu in hard wars with the Takeda. After the Mikatagahara defeat he was among loyal men who worked on retreat and recovery.
At Nagashino he fought the Takeda and helped win a battle that mixed gun units with new tactics. His troops were reputed for mobility and charge.
He shone in the Komaki-Nagakute war against Hashiba Hideyoshi, pressuring Hideyoshi's side. After Ieyasu's move to the Kanto he kept trust as a fudai elder.
After the Odawara campaign he received 100,000 koku at Tatebayashi in Kozuke. Amid Tokugawa expansion before Sekigahara he held a key base.
At Sekigahara he served as army inspector with Tokugawa Hidetada on the Nakasendo, took part in attacking the Sanada at Ueda, and arrived late to the main battle. Afterward he was still trusted.
When Ieyasu became shogun, Yasumasa backed the bakufu as a fudai daimyo. As war gave way to civil rule, the role of meritorious vassals was also changing.
He died of illness at Tatebayashi Castle at fifty-nine. Known for loyalty and valor, he lived on as one of the Tokugawa Four Heavenly Kings. Descendants later moved at times to places such as Himeji.
Imagawa YoshimotoTokugawa IeyasuIi NaomasaTokugawa HidetadaSakai TadatsuguHonda TadakatsuHori Hidemasa
Satake YoshishigeOda Nagamasu (Urakusai)Honda TadakatsuNene (Kōdai-in)Takayama UkonMōri TerumotoHori HidemasaSuminokura Ryōi
People of the Sengoku/Azuchi-Momoyama period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.