Duke Ding (魯定公) was the predecessor of Duke Ai (哀公) as the ruler of Lu, and reigned from around 509 to 495 BCE. Although responsible for elevating Confucius to his highest official position as Minister of Justice (大司寇) of Lu, the duke was ultimately at least indirectly responsible for Confucius’s decision to go into exile because of his inability to control the Three Families, who were the de facto rulers of the state. Indeed, Duke Ding was said to be so weak that he was the kind of ruler who “held the blade of the sword and offered the handle to his enemies.”
In 501 BCE, Duke Ding appointed Confucius as Minister of Works (司空) following his successful stint as governor of Zhongdu (中都宰), a district located in modern-day Wenshang County in Shandong province.
One year later in 500 BCE, the duke asked Confucius to take charge of the preparations for a meeting at Jiagu with Duke Jing of Qi (齊景公), to formalize a peace treaty between the two states. To protect Duke Ding from a planned kidnap by Duke Jing’s retinue, Confucius stationed troops near to the meeting place and after succeeding in foiling plot helped his ruler secure an apology from Duke Jing together with the return of some disputed land that he had captured from Lu.
Following this great diplomatic victory, Duke Ding developed an even closer relationship with Confucius and subsequently appointed him as Minister of Justice (大司寇) for Lu. In 498 BCE, on the advice of Confucius, the duke moved to weaken the power of the Three Families, the Jisun (季孫), Mengsun (孟孙), and Shusun (叔孫), by ordering them to disarm and dismantle the fortresses they had built in violation of the law.
Appearances in the Analects of Confucius
Book 3, Chapter 19
Duke Ding asked: “How should a lord treat his ministers? How should ministers serve their lord?” Confucius replied: “A lord should treat his ministers in accordance with ritual; ministers should serve their lord with loyalty.”