Tomomasa Oyama

Tomomasa Oyama was the second head of the Oyama clan and a leading early Kamakura gokenin, serving Minamoto no Yoritomo from 1180. In 1183 he feigned alliance with Shida Yoshihiro and ambushed him at Nogi-no-miya in Shimotsuke; wounded, he still routed the rebel with his brother.

He fought the Taira under Minamoto no Noriyori, including Dan-no-ura in 1185, and joined the Ōshū campaign of 1189. He held the Shimotsuke and Harima shugo posts, took the tonsure in 1234 and died in 1238 aged 84.