Sima Yi (Zhongda) was a Cao Wei general and politician. His descendants eventually overthrew Wei, formed Jin and unified China for a brief period (until they were kicked southwards by northern invaders because of the state's own initial weakness and civil war ).
In Romance of the Three Kingdoms, he was well known for his rivalry against Zhuge Liang. This is no different in Shin Sangoku Musou. His Yokoyama Mitsuteru counterpart is best known as the source of the ”Wait. Don't be upset. This is Zhuge Liang's trap” meme.