Xu You (simplified: 許攸, traditional: 許攸, pinyin: Xǔ Yōu) was from Nanyang and had been a childhood friend of Cao Cao. He served Yuan Shao as an adviser. Before the Battle of Guandu (200), Xu You defected to Cao Cao and revealed that Yuan Shao’s supply depot at Wuchao was lightly defended. Cao Cao led a raid on Wuchao, burned the supplies, and turned the campaign in his favour; Jia Xu’s biography notes that “Xu You came to surrender and offered a plan.” After Cao Cao took Ye (204), Xu You behaved arrogantly—calling Cao Cao by his childhood name and boasting of his merit—and was killed. Sources differ: either Xu Chu slew him for disrespect, or Cao Cao had him executed. Du Xi once remonstrated with Cao Cao not to attack the Guanzhong general Xu You (a different Xu You who held troops and slighted Cao); that episode concerns a different figure or a conflated account.
Xu You 許攸
Yuan Shao's adviser and childhood friend of Cao Cao; defected to Cao Cao before Guandu and advised the raid on Yuan's supply depot at Wuchao; later killed by Xu Chu for disrespect or executed by Cao Cao.