Empress Cao
Cao Guojiu is believed to be a descendant of Cao Bin, a general of the early Song dynasty, and a younger brother of Empress Cao, the wife of Emperor Renzong of the Song dynasty. As none of Emperor Renzong's sons survived their father, the emperor designated a younger male relative, who later became Emperor Yingzong, as his successor. As such, Cao could not have been a maternal uncle of Emperor Yingzong, so his "Imperial Uncle" status seemed ambiguous. However, as the Chinese character "jiu" (), which means "maternal uncle", can also mean "wife's brother", it is believed that the latter meaning should apply to Cao. In other words, Cao was the "Imperial Brother-in-Law" of Emperor Renzong rather than an "Imperial (Maternal) Uncle" of any Song dynasty emperor.