Name: Sima Yi
Weapon: Feathered Fan
Family: Sima Zhao (son), Sima Shi (Son)
Sima Yi is a master strategist and is one of the "demonic" characters in the game. He is the rival of Zhuge Liang, who is also a master strategist, and who seems to be the "kindest" version of Sima Yi. Sima Yi and Zhuge Liang seem to be like Yin and Yang. Sima Yi fights on the side of evil, and he has an outfit an a voice to match. His outfit is a long, purple outfit, and his voice is high raspy, much like TV super villians' voices are. His weapon is a "fan" of black feathers, which is the complete opposite of Zhuge Liang, who also has a "fan" of feathers, but his feathers are white. They also have the exact same attack, shooting lasers from their fans. These two men seem to be like twins, one evil, and one good. However, there are a few small differences between them to make them look better than the other one. For instance, Zhuge Liang doesn't fight much, so he is seen as weak, whereas Sima Yi fights all the time, however, when you do have to fight Zhuge Liang, he is stronger than Sima Yi. Sima Yi also doesn't have a love interest, meaning he's single, but Zhuge Liang has a wife named Yue Ying, who is a top inventor and who invents the weapons to help them win most of the battles. So between the two, Zhuge Liang is probably the strongest.
Sima Yi fought under Cao Cao, then fought under Cao Pi when Cao Cao was killed. He follows his leaders religiously, never complaining about them, but at the end of his story in Dynasty Warriors 5, Sima Yi walks away from Cao Pi and Zhen Ji, whispering under his breath, "Enjoy your victory while you can...because soon, this will all be mine..." revealing that he actually hates his leaders and wants to take everything away from them. Which in history, he did. Cao Cao died early in his life from a brain tumor, after that, Cao Pi took the throne. However, when Cao Pi retired from being the leader, it was Sima Yi who took the throne.
In Dynasty Warriors 6, it is revealed that Sima Yi has a son, Sima Zhao. However, Sima Yi has no spouse, and he clearly states that Sima Zhao is his blood related son. So it is still wondered who Sima Zhao's mother is.