Wèi Yán (魏延, 175–234), courtesy name Wéncháng (文長), was a distinguished officer of Shu.

The novel Romance of the Three Kingdoms suggested that Wei Yan originally served as a mid-ranked military officer of Liu Biao, but the history books didn't officially recognize that.

He joined Liu Bei's army after Liu captured Changsha in about 209. His talent helped him to become a major general of Liu's Army in very few years. Liu Bei offered him the place of chief executive at Hanzhong (漢中) in 219, making him the sixth most important military man of the kingdom after the Five Tiger Generals.

After Liu Bei's death in 223, Zhuge Liang employed him for the war with Wei. He had suggested some radical plans in order to win the war but Zhuge Liang rejected them.

When Zhuge Liang died in 234, some officers under him (including Jiang Wei) killed Wei Yan, in the title of "rebellion".

Both the history and the novel suggested that Wei Yan intended to attack Sima Yi, the general of Wei, but people including Jiang Wei objected to the plan and ordered Wei Yan to retreat. Wei refused and thus attempted to kill those officers by burning down the wooden walkway and preventing them from returning to Shu. Those officers thus claimed him "rebelling" and killed him with a plot.

In the novel, Zhuge Liang had foreseen Wei Yan's revolt before his death, and secretly left instructions to be carried out to deal with it when it came. When Wei Yan rebelled, Ma Dai pretended to join him, and earned his trust, so that later, following Zhuge's instructions, he was able to strike down Wei Yan from behind without the latter suspecting.

According to Sanguo Zhi, Wei Yan was a very arrogant man and others tended to avoid him. Some people believe that Wei Yan was an aggressive person, which is incompatible to Zhuge Liang. Moreover, Wei Yan's personality made Yang Yi fear him and finally decide to get rid of him. He was killed by Ma Dai.

Others believe that Zhuge Liang was unfairly biased against Wei Yan, beginning when Wei Yan rescued Huang Zhong from execution and surrendered a city to Liu Bei, slaying the prefect in the process. While Zhuge Liang welcomed Huang Zhong, he ordered Wei Yan executed, saying that anyone who would betray their lord so easily was untrustworthy. Liu Bei ordered Wei Yan's life spared and welcomed him into his forces. This is from the novel, of course. Wei Yan never slain Han Xuan because Han Xuan surrendered.

Based on the one example of Zhuge Liang's entrusting his student Ma Su to an important task despite Liu Bei's warning that he was unsuited for anything important, Wei Yan's supporters believe that this was simply another example of Zhuge Liang's poor judgement of character as opposed to his supreme judgement of warfare. It was said that even the great general Zhang He respected and feared Wei Yan's abilities.

In legend, Zhuge Liang was said to ask for an extension of his life in Wuzhang Plains, pointing to a candle and saying, if the candle continues to burn, he will continue to live; if it was extingushed, he would perish. However, Wei Yan knocked the candle over, and Zhuge Liang died shortly after.