Jia Xu
During his service under Cao Cao, Jia Xu made three important contributions. First, during the Battle of Guandu, he urged Cao Cao to switch from being on the defensive to adopting an offensive stance, which ultimately led to Cao Cao's decisive victory over Yuan Shao. Second, during the Battle of Tong Pass in 211, he suggested to Cao Cao to pretend to agree to make peace with the northwestern warlords Han Sui and Ma Chao, and then sow discord between them. Cao Cao heeded his suggestion, successfully stirred up internal conflict among the warlords, and then used the opportunity to defeat them. Thirdly, in the 210s, when Cao Cao's sons Cao Pi and Cao Zhi were fighting to be their father's successor, Jia Xu indirectly helped Cao Pi by giving him advice and hinting to Cao Cao that he should choose the older son to be his heir apparent. After Cao Cao's death in 220, Cao Pi ended the Eastern Han dynasty by forcing Emperor Xian to abdicate the throne to him, and founded the state of Cao Wei with himself as the emperor. As an expression of gratitude to Jia Xu, Cao Pi appointed him as Grand Commandant – one of the top three positions in the Wei government – and promoted him to a district marquis. Between 220 and 223, Jia Xu advised Cao Pi against attacking Cao Wei's rival states, Eastern Wu and Shu Han, and focus on internal development. However, Cao Pi ignored his advice and invaded Wu, but ended up sustaining heavy losses and not making any significant gains. Jia Xu died in 223.