The Son of Heaven (天子 tiānzǐ) was the sovereign’s ritual title, linking his rule to the Mandate of Heaven. Whoever controlled the person of the Son of Heaven could claim to act in the court’s name.
Holding the Son of Heaven to command the lords
After Cao Cao brought Emperor Xian to Xuchang in 196, his adviser Xun Yu had urged welcoming the emperor to secure legitimacy. Cao Cao then issued edicts and appointments in the emperor’s name—the strategy later summarised as ‘holding the Son of Heaven to command the lords’ (挟天子以令诸侯). Rivals who defied the court could be cast as rebels; those who submitted accepted Cao’s authority. The phrase appears in the sources in connection with Cao Cao’s rise and with the dilemma faced by Sun Quan’s court before the Battle of Red Cliffs: whether to resist Cao and risk being labelled disloyal, or to submit.