Zhu Ci
Liu Ji was born in 757 — during the Anshi Rebellion, when Fanyang Circuit (范陽, later known as Lulong), where his father Liu Peng was from, was governed by the rebel state Yan, which rivaled Tang Dynasty, then ruled by Emperor Suzong. Liu Ji had at least two younger brothers, Liu Yong () and Liu Yuan (). After Yan's destruction in 763, Fanyang, renamed Lulong, was nominally reintegrated into Tang, but was then governed successively by Li Huaixian and Zhu Xicai, both of whom ruled it "de facto" independently from the Tang imperial government. In 772, Liu Peng's cousin Zhu Ci became military governor after assassinating Zhu Xicai, and Liu Peng thereafter successively served under Zhu Ci and his brother Zhu Tao.