During the late Spring and Autumn period, the Duke of Jin's power had weakened, with real control divided among six ministers: the Fan, Zhonghang, Zhi, Han, Wei, and Zhao clans. After the Fan and Zhonghang were eliminated, the remaining four—Zhi, Han, Wei, and Zhao—each sought greater territory and influence. Zhi Bo then allied with Han Kangzi and Wei Huanzi to attack Zhao Xiangzi. However, Zhao Xiangzi secretly persuaded Han and Wei to switch sides, and together they turned on Zhi Bo, annihilating his clan and dividing his lands.
After the fall of the Fan clan, the warrior Yu Rang became a trusted retainer of the lord Zhibo, who valued his talents deeply. When Zhibo was slain by Zhao Xiangzi, Yu Rang fled to the Stone Chamber Mountains, vowing, "I will kill Zhao Xiangzi and avenge my lord!"
So he changed his name and appearance, disguised himself as a convicted criminal, and hid a dagger on his person before sneaking into the toilet of Zhao Xiangzi's mansion, planning to strike when Zhao Xiangzi came to relieve himself. That day, when Zhao Xiangzi entered the latrine, he suddenly sensed a strange presence and immediately ordered his guards to search, discovering Yu Rang.
Zhao Xiangzi asked, "Who are you, daring to hide a dagger and come to assassinate me?" "I am a retainer of Earl Zhi, and I must avenge my master!" Yu Rang replied. "He is a rebel assassin—kill him!" one of Zhao Xiangzi's ministers urged. Zhao Xiangzi waved his hand and said, "Earl Zhi has no descendants. Now Yu Rang comes to avenge him—he is truly a righteous man. We cannot kill him; let him go!" Thus, Zhao Xiangzi ordered Yu Rang's release and asked, "I have freed you—can you set aside past grievances?" Yu Rang answered, "You freed me—that is your kindness; I avenge my master—that is my honor!" Zhao Xiangzi's men found Yu Rang utterly unreasonable and wanted him dead, but Zhao Xiangzi said, "I have already promised to release him—how can I break my word? Just be careful to avoid him from now on!"
After returning home, Yu Rang spent his days consumed with thoughts of revenge. Knowing that Zhao Xiangzi would be on guard against him, he decided to alter his appearance beyond recognition. He shaved off his beard and eyebrows, then lacquered his head, face, and body to resemble a leprous beggar covered in sores. Disguised, he went to the marketplace to beg, and even his closest friends failed to recognize him.
His wife went to the market to look for him. Hearing a beggar's voice, she exclaimed in surprise, "That is my husband's voice!" She hurried forward to see, and upon seeing Yu Rang, said, "The voice sounds so familiar, yet the person is not him." Then she left.
After his wife left, Yu Rang, worried that his voice might be recognized by her or other acquaintances, swallowed burning coals to deliberately scar his throat and render his voice hoarse. This way, even when his wife saw him, she could not identify him at all.
Yu Rang arrived in Jinyang, the territory of Zhao Xiangzi, and waited for his chance. One day, he learned that Zhao Xiangzi would surely pass over Red Bridge during his travels, so he hid a dagger and lay in ambush beneath the bridge, ready to strike. But he was discovered and captured once again. Though Yu Rang had altered his voice and appearance, Zhao Xiangzi still recognized him. Zhao Xiangzi cursed, "I spared you last time, yet today you come to assassinate me again. I cannot release you again. Guards, take him away and behead him!"
Yu Rang wept bitterly, tears of blood streaming from his eyes. One of Zhao Xiangzi's men asked him, "Why are you crying? Are you afraid of death?" "It's not that I fear death," Yu Rang replied. "I am thinking that after I die, there will be no one left to avenge Zhi Bo!"
Zhao Xiangzi heard this and demanded, "You were once a retainer of the Fan family. When Fan was killed by Zhibo, you endured shame and clung to life—not only did you refuse to avenge Fan, but you even defected to Zhibo. Yet now that I have killed Zhibo, you are determined to avenge him. Why is that?"
"Fan treated me as an ordinary man, but Earl Zhi regarded me as a soulmate. A warrior dies for his soulmate, so of course I must avenge Earl Zhi!" Yu Rang declared. Zhao Xiangzi was deeply moved, unbuckled his sword, and sighed, "Your heart is as firm as iron and stone. I will not pardon you again. Take your own life!"
Yu Rang took the sword and said to Zhao Xiangzi, "I failed twice in my assassination attempts, and my resentment cannot be vented. If you, my lord, would remove your outer robe and let me strike it a few times to fulfill my desire to avenge my master, then I will die with my eyes closed!"
Zhao Xiangzi greatly admired Yu Rang's integrity and immediately took off his embroidered robe, handing it to Yu Rang. Yu Rang placed the robe on the ground, stepped forward and slashed it three times, crying out, "Zhi Bo, now I can come to the underworld to see you!" With that, he drew his sword and committed suicide.
Later, the idiom "lacquer body, swallow charcoal" came to describe deliberately altering one's voice and appearance to avoid recognition, or sacrificing oneself for one's master.
Source: *Strategies of the Warring States*, Chapter "Strategy One of Zhao"
Meaning of the Idiom: Later, the Chinese idiom "漆身吞炭" came to describe how deliberately altering one's voice and appearance to avoid recognition, or sacrificing oneself for one's master.