Wu Mengzi (吳孟子) was the name that Duke Zhao of Lu (魯昭公) gave to his wife to mask the fact that he had violated a strict ritual convention by marrying a woman with the same family name (姬/Jī) as his own.
Wu Mengzi literally means “Mengzi of Wu”, which is the name of the state that she came from. Her original name was Ji Mengzi 姬孟子. Even though the duke and his wife were not related by blood, he was criticized for his failure to respect ritual by marrying her and attempting to sweep it under the carpet by changing her family name.
Appearances in the Analects of Confucius
Book 7, Chapter 30
The Minister of Justice of Chen asked: “Did Duke Zhao understand ritual?” Confucius said: “Yes, he understood the rites.” Confucius withdrew. With a bow, the minister invited Wuma Qi to come forward and said to him: “I’ve heard it said that a true leader is never biased. But isn’t your master biased after all? The duke took a wife from the state of Wu; but because she had the same family name, he called her Wu Mengzi. If the duke understood ritual, who doesn’t understand it?” Wuma Qi reported this to Confucius. Confucius said: “I’m fortunate indeed: whenever I make a mistake, there’s always someone on hand to let me know about it.”