張郃
Later that year, during the Battle of Guandu, Cao Cao led a successful raid on Yuan Shao's supply depot at Wuchao (烏巢) and set fire to the supplies. Zhang He and Gao Lan (高覽), two of Yuan Shao's officers, wanted to lead troops to attack Cao Cao at Wuchao and salvage whatever supplies they could. However, Guo Tu strongly objected to this plan and proposed that they attack Cao Cao's main camp instead to divert Cao Cao's attention away from Wuchao. Yuan Shao heeded Guo Tu's advice and ordered Zhang He and Gao Lan to lead troops to attack Cao Cao's main camp. When news reached Yuan Shao that Zhang He and Gao Lan had failed to capture Cao Cao's main camp, Guo Tu became fearful because his idea had gone wrong. He then accused Zhang He and Gao Lan of not doing their best because they were planning to defect. After Zhang He and Gao Lan heard about it, they were so angry that they led their troops and defected to Cao Cao's side.