Cheng Yu's original given name was "Li" () but he changed it to "Yu" (昱; literally "lifting the sun") after he had a dream about the sun on top of
Mount Tai. He was from
Dong'e County, which is in present-day
Shandong. There is nothing recorded in history about his early life; he was known for his courage in the areas around his hometown when he was in his early 40s. When the
Yellow Turban Rebellion broke out in the 180s, a
county magistrate, Wang Du, burnt down the food stored in the warehouse and instigated his subordinates to seize the city. The county prefect escaped the city and went into hiding, while the town residents took their families eastward and camped beside a mountain. After receiving intelligence from his spies that Wang Du had moved out and camped 1.3 to 1.6 miles away from the city, Cheng Yu reported to and told a local parvenu, Xue Fang, that Wang Du must not have the ability to control the situation, so they should retrieve the prefect and reoccupy the city. Xue Fang agreed to Cheng Yu's plan, yet the commoners refused to comply, wherein Cheng Yu angrily said: "Stupid commoners lack the ability to plan." He then plotted with Xue Fang, and secretly sent several cavalry holding streamers to the hilltop, where they rode down toward the civilians. Xue Fang and his men then screamed upon seeing the riders, making the commoners mistake them for Yellow Turban rebels. Led by Xue Fang, the mass kept running until back into the city, where they realised that the rebels were not so terrifying and started to defend the city with the prefect, whom Cheng Yu found later. Seeing the inhabitants had come back, Wang Du launched an attack, but was foiled by Cheng Yu's defences. After some time, Wang Du could no longer hold on and intended to move elsewhere. Cheng Yu then led a sudden attack when Wang Du was packing, dealing him a major blow which enabled the survival of Dong'e County. In 192,
Liu Dai, the Inspector of
Yan Province, invited Cheng Yu to join his administration but Cheng Yu refused. At the beginning, Liu Dai had very good relationship with the warlords
Yuan Shao and
Gongsun Zan, wherein Yuan Shao sent his family to reside with Liu Dai while Gongsun Zan sent a detachment of elite cavalry to help Liu Dai fight the Yellow Turbans in the area; however, Yuan Shao and Gongsun Zan became bitter enemies later, and were way more powerful than Liu Dai, who was forced to pick a side. Liu Dai then sought advice from Cheng Yu, who told the former that asking for help from Gongsun Zan was like requesting someone to save a drowning child from afar. He further analysed that Gongsun Zan, who had recently gained a minor military victory over Yuan Shao, would eventually lose to the latter. Therefore, it was not wise to enjoy a short-term benefit without a careful long-term plan. Liu Dai agreed with Cheng Yu's speech and severed ties with Gongsun Zan, who ordered his cavalry in Yan Province to return to his base in
You Province. Just as Cheng Yu had predicted, Gongsun Zan soon suffered a heavy defeat by Yuan Shao before his cavalry could even join the battle. Liu Dai then asked Cheng Yu to become his officer, and offered him the position of a Cavalry Commandant, but Cheng Yu again refused employment. ==Coming to serve Cao Cao==