Xu You 許攸

Xu You was a strategist under Yuan Shao. During the Battle of Guandu, he defected to Cao Cao and told him about Yuan Shao's poorly defended supply base in Wuchao, eventually leading to Yuan Shao's defeat.

Life
Not much was known about him before he joined Yuan Shao, but he was known to be greedy and a friend of Cao Cao. He did not participate in the debate for the next heir of the Yuan family but he was hated by his fellow peers due to his greediness and thus, having his wife arrested as a warning. Shen Pei told Yuan Shao about his family that they were locked up for charges of corruption which made Yuan Shao more careful then dealing with him.

Xu You became an adviser at the Battle of Guan Du and kept advising Yuan Shao to send troops to defend their lightly defended supply depot at Wu Chao. Yuan Shao however did not heed his advise and told him, "You still have the cheek to present your strategies in front of me?" Xu You was furious at his response and quickly left Yuan Shao's services and joined Cao Cao.

During Cao Cao's services, he told Cao Cao about Yuan Shao's granaries at Wu Chao and advised him to attack there to completely drain the entire morale of the Yuan army. Cao Cao's men were suspicious of him but Xun You and Jia Xu urged Cao Cao to take his plan into action. The plan worked and Wu Chao was all burnt down by Cao Cao's men as they disguised themselves as Yuan Shao's men.

In 202, Yuan Shao died by illness and Cao Cao paid respect to his tomb. Xu You however showed no remorse nor respect at all and insulted Yuan Shao so Cao Cao put him to death afterward.