Although he was an official under Cao Cao, Sima Yi put his true talents to work under Cao Pi and Cao Rui. They relied on him for his brilliant political insight and strategy. Under Cao Cao's command, he was successful in the battle against Zhang Lu.
     When Liu Bei became Prince of Hanzhong, Sima Yi turned a wary eye to the south. He negotiated with Sun Quan and persuaded him to attack Guan Yu at Jingzhou. Thereby Sun Quan captured and killed Guan Yu. Sima Yi's greatest challenger was Zhuge Liang, the advisor who inherited the Shu kingdom from Liu Bei. When Zhuge Liang began his incursion of the north, Sima Yi beat back his general Ma Su and launched a stalling procedure on the Wuchang Plain. He was also successful in the battle against Meng Da who planned to betray Wei and help Zhuge Liang. Sima Yi was accomplished in military tactics and strategy and commanded his men skillfully. As a result, Zhuge Liang could not score a decisive victory against Sima Yi, who was very good in defense. Frustrated by the standstill, Zhuge Liang sent Sima Yi a woman's headdress, hoping to anger him. Yet, his efforts were in vain. As time dragged by, there was news that Zhuge Liang was ill and dying.
     Sima Yi waited for his opponent to die before he went in pursuit of the Shu army. He pursued them when they began to retreat into Shu. Suddenly Zhuge Liang appeared before him, and he fled for his life. In fact, he was scared away by a wooden image of his deceased foe. Word spread that, "even a dead Zhuge Liang can make a live Sima Yi run." When Sima Yi heard this rumor he laughed and said, "When Zhuge Liang was alive I could calculate each move, now that he's dead I am defenseless."
     When Gongsun Yuan rebelled against Wei, Sima Yi led the Wei army and completely destroyed the rebels. Later, Sima Yi gained military power in a contest with Cao Shuang and became Prime Minister of Wei. In 251 AD, Sima Yi rooted an uprising led by Wang Ling and he died at the same year. He helped four generations of the Cao family and established the Jin dynasty.