King Wei of Qi (Chinese: 齊威王; pinyin: Qí Wēi Wáng), whose personal name was Tian Yinqi (田因齊), was the king of the northern Chinese state of Qi during the Warring States period, when Qi was one of the most powerful states in China. He reigned from 356 to 320 BC. or according to another source from 378 to 343 BC.

His successor was King Xuan of Qi. In the Intrigues of the Warring States, the strategist Su Qin is quoted as telling the king of Qin: "Kings Wei and Xuan of Qi were the worthiest rulers of their age. Their power was great and their lands were broad. Their states were wealthy and their citizens capable. Their generals were aggressive and their troops strong."

King Wei was judicious and measured in his actions toward his subordinates. At one point he was told repeatedly by his spies that one of his generals, Zhangzi, had surrendered to the enemy, Qin. King Wei refused to believe that Zhangzi had deserted. Sure enough, "a short while later it was reported that Qi had won a great victory. The king of Qin proclaimed himself a vassal of the western borders and made his apologies to Qi." King Wei said that he always knew Zhangzi was faithful and cited this story in his defence.

According to another story, King Wei proclaimed that "To all ministers, officers and citizens who criticize my faults in front me, they will get the highest reward; those who remonstrate with me in writing will be given the next highest reward, and to those who overhear criticism of me and convey it to my ears will go the least reward." It was said that initially, "the doorway to the king's chamber looked like a marketplace" but after a year, "none who spoke to the king had petitions to present" [because the problems had already been solved]. "When [the states of] Yan, Zhao, Han and Wei heard of this they all came to court at Qi."

King Wei employed Sun Bin as chief military advisor. Sun Bin had been punished with mutilation of his knees in Wei at the instigation of his enemy Pang Juan. King Wei's commander Tian Ji recruited him to come to Qi. As Sun Bin could not sit on a horse, he refused when King Wei offered him the actual command of the army. Sun Bin wrote Sun Bin's Art of War, in which King Wei and Tian Ji question Sun Bin on strategy and tactics. Sun Bin was influential in devising the strategy for the Qi triumph at the Battle of Maling in 342 BC, which considerably weakened the rival state of Wei. Pang Juan died there. "Late in his reign, he sent out armies against Qin and Zhao."

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