Unofficially the '6th Tiger General of Shu', Wei Yan possessed superior combat skills. He spent many years of service under Shu as first class warrior. Wei Yan first served under Liu Biao, but he was devoted to Liu Bei. He played a key role in the overthrow of Liu Zong; a Cao Cao adherent. After Liu Biao's death, Liu Zong succeeded him, but he was forced and surrendered under the influence of Cao Cao. Although he served Liu Zong at the time, Wei Yan opened the castle gates to Liu Bei's army. In the course of fighting off Wen Pin, Wei Yan lost sight of Liu Bei and ended up serving Han Xuan in Changsha. Once again, he rebelled against his leader. By slaying Han Xuan, he rescued Huang Zhong from the executioner's blade and surrendered Changsha to Guan Yu. Thereafter, he served Liu Bei, but Zhuge Liang never trusted him and predicted that he was not a man of loyalty.
     Wei Yan accompanied Liu Bei on his expedition into Shu and then into Hanzhong which were successful. He also aided Zhuge Liang in his victorious suppression of southern Mang tribe of Shu. In all the northern expeditions, Wei Yan was highly used as the frontline general in fighting Wei. After the deaths of five tiger generals, Wei Yan was considered as the best warrior in Shu. For this reason, Zhuge Liang had to use him. In one of his actions, he killed Wang Shuang; top warrior of Wei with one strike of his blade. At first northern expedition, Wei Yan advised Zhuge Liang to attack Changan straight ahead, but he felt that he was insulted when he was ignored. From then on, he persisted in slandering Zhuge Liang as a coward.
     Prior to his death, Zhuge Liang gave Yang Yi a silken bag with instructions as to what to do after his death. After Zhuge Liang passed away, a power struggle between Wei Yan and Yang Yi eventuated into rebellion. Wei Yan disobeyed orders and led his troops into battle. He had the help of Ma Dai at first, but Ma withheld a secret plan that Zhuge Liang divulged to him before dying. They seemed to develop a close friendship, but when he least expected it, Ma Dai slew Wei Yan, fulfilling Zhuge Liang's last will.