Becoming Liu Bei's Chief Adviser Liu Bei appointed Fa Zheng as the Administrator () of Shu
Commandery () and General Who Spreads Martial Might (). Fa Zheng oversaw administrative affairs in the vicinity of
Yi Province's capital
Chengdu. While Zhuge Liang was promoted to administer internal affairs, Fa Zheng served as Liu Bei's chief adviser. Following Liu Bei's victory over Liu Zhang, his subordinates urged him to take for wife Liu Mao's widow. However Liu Bei refused on the basics that he and Liu Mao were of the same family. Fa Zheng then to convince him said: "In the ancient times, lady
Huai Ying first married the
Duke Huai of Jin and later married his own brother, the
Duke Wen of Jin. If the marriage of a widow between brothers happened by the past then why not for you and Liu Mao who are not close kinsman?" Liu Bei agreed with him and married Lady Wu. During this period of time, Fa Zheng repaid all of his previous debts, good or bad. He would not forget those who showed him even a little kindness but also abused his power by taking revenge against those who offended him before. And by killing those who harmed him without the legal authority. Someone approached
Zhuge Liang, another of Liu Bei's key advisers, and urged him to restrict Fa Zheng's influence by advising their lord to take action against him. However, Zhuge Liang replied, "When our lord was in
Gong'an, he was wary of
Cao Cao's influence in the north and fearful of
Sun Quan's presence in the east. Even in home territory he was afraid that
Lady Sun might stir up trouble. He was in such a difficult situation at the time that he could neither advance nor retreat. Fa Xiaozhi supported and helped him so much that he became his own wings (翼), such that he is now able to fly high and no longer remain under others' influence. How can we stop Fa Zheng from behaving as he wishes?" Zhuge Liang was aware that Liu Bei greatly favoured and trusted Fa Zheng, which was why he refused to intervene in this matter. The historian
Sun Sheng criticised Zhuge Liang's attitude towards Fa Zheng's abuse of power and called it a "lapse in justice". He felt that no subject should be above the law, regardless of how great his past contributions were. While Tang Geng (), a scholar from the
Song dynasty, in his work called the
Three Kingdoms Miscellaneous Cases (三國雜事;
Sanguo Zashi) compared Fa Zheng to Fan Ju (),
Li Guang and Guo Jin (). The three of them were allowed to settle their personal grudges and rendered great achievements for their States. Tang Geng commented that this is how rulers of the past made use of their outstanding and heroic individuals. That they had their own conceptions of righteousness. Tang Geng called Sun Sheng shortsighted for not seeing this.
Role in the Hanzhong Campaign In 217, Fa Zheng urged Liu Bei to attack
Hanzhong Commandery, which was originally under
Zhang Lu's control but was
conquered by
Cao Cao in 215. He pointed out Hanzhong's strategic importance and said that it was an opportune moment for Liu Bei to seize Hanzhong from Cao Cao's generals
Xiahou Yuan and
Zhang He. He told Liu Bei: "Cao Cao with a single strike was able to submit Zhang Lu into surrender and acquire Hanzhong, however he did not press his advantage to conquer Ba and Shu. Instead he returned North and left Xiahou Yuan and Zhang He. This cannot be an error of his part or because of a lack of strength, but rather because he met some internal problems and must solve them. Now Xiahou Yuan and Zhang He can't compare against our army. If we advance, we will surely capture them. Then we can collect grains, fill our storehouse readying ourselves for any opportunities. If we are successful we can vanquish the enemy and restore the ruling House, otherwise we can expand our borders into the Liang province and in any case we would have gain a most important position to defend and prepare ourselves. Heaven is on our side, you must not lose this chance." Liu Bei accepted his plan and started the
Hanzhong Campaign with Fa Zheng following him. In 219, during the
Battle of Mount Dingjun, when Xiahou Yuan led troops to attack Liu Bei's camps at Dingjun and Xingshi mountains, Fa Zheng suggested Liu Bei to strike the enemy. Liu Bei ordered his general
Huang Zhong to lead his men on a charge down the mountain towards Xiahou Yuan's forces, with war drums beating in the background. Huang Zhong defeated and killed Xiahou Yuan in the midst of battle. Later, when Cao Cao was leading his forces from
Chang'an to reinforce Hanzhong, he received news about the strategy proposed by Fa Zheng to Liu Bei to attack Hanzhong. He remarked, "I know Xuande (Liu Bei) is not capable of doing this. He must be following somebody's advice." According to the
Chronicles of Huayang, Cao Cao also said: "How could it be that among my army of bold heroes, none could find a strategy that would overcome this Fa Zheng?" The historian
Pei Songzhi commented that Cao Cao made that former remark – which suggests that Liu Bei was not wise enough to notice Hanzhong's strategic importance – because of his personal disdain for Liu, and that it should not be taken seriously. He felt that a lord acting on his adviser's suggestion should not be interpreted as a sign that the lord was not wise enough to make his own judgment. He pointed out that Cao Cao himself also followed the advice of his adviser
Guo Jia. ==Death and postmortem events==