Records of the Three Kingdoms
Chen Gong, courtesy name Gongtai, was from Dong commandery. He worked with Cao Cao at first. In 194 he and Zhang Miao, governor of Chenliu, rebelled and brought Lü Bu into Yan Province. Cheng Yu and Xun Yu held three cities, so Cao Cao did not lose the whole base.
After that Chen Gong planned for Lü Bu. His proposals were often the firmer ones. Lü Bu hesitated, and the household pulled against the plans. In 198 Cao Cao besieged Xiapi and flooded it from the Yi and Si rivers. When Lü Bu surrendered, Chen Gong was brought bound before Cao Cao. Cao Cao said the mother and wife would be provided for. Chen Gong walked straight out to the execution and did not turn his head. Cao Cao wept and supported the family.
Romance of the Three Kingdoms
The novel makes Chen Gong the first man to see through Cao Cao. After Cao Cao kills Lü Boshe’s household by mistake he says he would rather wrong the world than let the world wrong him, and Chen Gong leaves. That speech and that departure are the moral start the book gives Cao Cao.
When Xiapi falls, Chen Gong refuses to submit and asks to die first. Cao Cao sends the mother and wife to Xu to be kept. The novel keeps that ending, and it also gives Chen Gong a series of plans Lü Bu will not take, to explain why Lü Bu had to lose.
Reference: Wikipedia · Chen Gong