Cáo Téng served as a eunuch in the Hàn dynasty court and acted as Cáo Cāo's adoptive grandfather. He sold government positions at heavily inflated prices. Despite his advanced age, he wielded substantial political influence and confronted powerful adversaries without hesitation.

During an imperial audience, Cáo Téng indirectly accused the influential eunuch Zhāng Ràng—present in the room—of corruption, citing inappropriate conduct with women and excessive sexual desires stemming from castration, though he avoided naming him explicitly. When the Emperor proposed banishment for such offenses, Cáo Téng demanded execution instead. After the audience, he privately warned Zhāng Ràng that any harm to Cáo Cāo would trigger his pursuit of Zhāng Ràng into the afterlife. This encounter highlighted his protective stance toward his grandson and his assertive use of court authority.