Records of the Three Kingdoms
Xun Yu, courtesy name Wenruo, was from Yingyin in Yingchuan. He left Yuan Shao, joined Cao Cao, and was compared to Zhang Liang. In 196 he urged Cao Cao to welcome Emperor Xian. Cao Cao then had the legal standing of Xu. When the grain ran short at Guandu and Cao Cao thought of retreat, Xun Yu wrote and told him to hold on.
In 212 Dong Zhao and others proposed that Cao Cao become Duke of Wei and receive the nine bestowments. Xun Yu opposed it in private. He held that Cao Cao had risen in the name of supporting the court and settling the state, and should not do this. He was kept with the army at Shouchun and soon died of worry. Pei quotes another account: Cao Cao sent an empty food box, and Xun Yu drank poison. Both accounts exist. Neither should be treated as the only one.
Romance of the Three Kingdoms
The novel prefers the empty box and the poison, and makes Xun Yu a Han minister whom Cao Cao drives to death. His scenes in the tent are usually steady advice, less sharp than Guo Jia’s.
Welcoming the emperor and the letter to hold at Guandu both remain.
Reference: Wikipedia · Xun Yu