Zhang Yizhi (張易之) (died February 20, 705), formally the Duke of Heng (恆公), nickname Wulang (五郎), was an official of Wu Zetian's Zhou Dynasty who, along with his brother Zhang Changzong, became a lover of Wu Zetian and became very powerful late in her reign. Both he and his brother were killed in a coup that overthrew Wu Zetian in 705.
It is not known when Zhang Yizhi was born. It is known that his father Zhang Xizang (張希臧) had, at one point, served as the census officer of Tang Dynasty's capital prefecture Yong Prefecture (雍州, roughly modern Xi'an, Shaanxi) and was a distant nephew of the chancellor Zhang Xingcheng. His mother might be Lady Wei or Lady Zang. As per Tang regulations, Zhang Yizhi, as the son of an official, was able to get into a civil service career himself in his 20s, serving as the imperial director of horses (尚乘奉御, Shangcheng Fengyu). It was said that his skin at that time was white and beautiful, and that he was good at singing.
In 697, Zhang Yizhi's younger brother Zhang Changzong was referred to Wu Zetian, then ruling with the title of emperor—the only woman in the history of China recognized for doing so—by Wu Zetian's daughter Princess Taiping, to be Wu Zetian's lover. Zhang Changzong further told Wu Zetian that Zhang Yizhi was even more skillful than he was, and so Wu Zetian took Zhang Yizhi as a lover as well. Both were repeatedly promoted—Zhang Yizhi as the deputy minister of military supplies (司衛少卿, Siwei Shaoqing) -- and both were said to often put makeup on their faces and dressing in a beautiful manner. Their mother or mothers were given titles as grand ladies, and Wu Zetian further ordered the chancellor Li Jiongxiu to serve as the lover for one of them. Even the most powerful officials flattered them, and referred them by endearing nicknames—Zhang Yizhi as Wulang and Zhang Changzong as Liulang (implying that Zhang Yizhi was the fifth-born son and Zhang Changzong was the sixth-born son of Zhang Xizang).