Masamitsu Oyama

Masamitsu Oyama was a late Heian to early Kamakura warrior and founder of the Oyama clan, whose estates around the Shimotsuke capital made him leader of its largest warrior band. Born into Musashi's Ōta house, he was first called Ōta Masamitsu and moved to the Oyama estate around 1150.

When Minamoto no Yoritomo rose in 1180, Masamitsu's wife Samukawa, Yoritomo's wet nurse, pledged his warriors to him; he and his sons served Yoritomo as gokenin. He died before 1199.