During the reign of Emperor Qin Er Shi (221-207 B.C.), Prime Minister Zhao Gao, driven by ambition, plotted day and night to usurp the throne. To test his influence and identify his opponents among the court ministers, he devised a plan.
One day in court, Zhao Gao had a stag brought in and, with a broad smile, said to the emperor, "Your Majesty, I present you with this fine horse."
The emperor replied, "Prime Minister, you are mistaken. This is clearly a stag. Why do you call it a horse?"
Zhao Gao remained calm and insisted, "Your Majesty, look more closely. This is truly a horse that can travel a thousand li a day."
Puzzled, the emperor asked, "How can a horse have antlers?"
Zhao Gao then turned to the ministers and declared loudly, "If His Majesty does not believe me, let the ministers decide."
The ministers were bewildered. Seeing Zhao Gao's sinister smile and piercing gaze, they understood his malicious intent. Some timid but righteous ministers remained silent, torn between conscience and fear. A few courageous ones insisted it was a stag. Meanwhile, Zhao Gao's usual sycophants immediately supported him, calling the stag a horse.
Afterward, Zhao Gao brutally punished the honest ministers who had opposed him, even executing some with their entire families.
This story, recorded in Sima Qian's Historical Records, gave rise to the idiom "calling a stag a horse," meaning to deliberately distort facts and mislead the public.