Ji Pingzi (died 505 BCE), whose surname was Jisun and given name Yiru, with the posthumous title "Ping," is historically known as Jisun Yiru, also referred to as Ji Shi, Jisun, or the Jisun clan. He served as the chief minister (prime minister) of the State of Lu during the Spring and Autumn Period.
Ji Pingzi's distant ancestor was Ji Chang (King Wen of Zhou). At the beginning of the Western Zhou dynasty when feudal lords were enfeoffed, Bo Qin (the eldest son of the Duke of Zhou, Dan) was appointed as the first ruler of the State of Lu, establishing its capital in Qufu. After Bo Qin, the throne of Lu passed through ten generations and sixteen rulers to Duke Zhuang of Lu. Duke Zhuang reigned for thirty-two years. His three younger brothers—Qingfu, Shuya, and Jiyou—had descendants who formed the Mengsun, Shusun, and Jisun families, respectively, historically known as the "Three Huan." In 662 BCE, after Duke Zhuang's death, Qingfu caused chaos in Lu, killing two successive Lu rulers within two years, sparking public outrage. At the time, it was said, "Until Qingfu is dead, Lu will never find peace." In 659 BCE, Jiyou used a stratagem to eliminate Qingfu and installed Prince Shen as Duke Xi of Lu. Upon his accession, Duke Xi granted Jiyou "the fields of Wenyang and the city of Fei." Fei (located at present-day Shangye Town, Fei County, Shandong Province) thereafter became his hereditary fief. After Jiyou's death, his descendants—Ji Wenzi, Ji Wuzi, Ji Pingzi, Ji Huanzi, and Ji Kangzi—successively served as chief ministers (Zhengqing) of Lu, effectively controlling the state's government.
In 535 BCE, Ji Pingzi succeeded his grandfather Ji Wuzi as chief minister of the State of Lu. During a sacrificial ceremony at the Duke Xiang Temple in Qufu, Ji Pingzi violated ritual propriety by using sixty-four dancers (the eight-row formation of eight dancers per row) for the performance—a privilege reserved for the Zhou king—and even sent all but two dancers to perform at his own residence. His arrogant and ritual-breaking behavior aroused discontent among some in Lu. In the autumn of 517 BCE, Duke Zhao of Lu led an attack on Ji Pingzi. Ji Pingzi climbed a high platform and begged the duke to imprison him in Fei, but the duke refused. He then asked for five chariots to flee, but was also denied. Ji Pingzi then allied with the Mengsun and Shusun families to attack Duke Zhao. The duke fled, first staying in the State of Qi, then in the Lu town of Yun, and finally in the Jin town of Qianhou.
Ji Pingzi's arrogance and overbearingness once provoked dissatisfaction from his retainer Nan Kuai. In 530 BCE, Nan Kuai conspired with others to rebel from Fei Yi. The following year, Ji Pingzi sent Lu's grand master Shu Gong to lead an army to suppress the rebellion, but they were defeated by the people of Fei. Ji Pingzi then adopted the advice of another Lu official, Ye Qufu, to appease the people of Fei. Soon, "the people of Fei rebelled against the Nan family." In 528 BCE, Nan Kuai fled in panic, and Fei Yi was returned to the Ji family.
In 505 BCE, Ji Pingzi (the de facto ruler of the State of Lu for thirty-one years) went on an inspection tour of the eastern region of Lu; on his return journey, he died of illness at Fangyi, which is present-day Fangcheng in Fei County.