Ban Chao (d. AD 102) enlisted the aid of the Kushan Empire, occupying the area of modern India, Pakistan, Afghanistan, and Tajikistan, to subdue Kashgar and its ally Sogdiana. When a request by Kushan ruler Vima Kadphises (r. c. 90–c. 100 AD) for a marriage alliance with the Han was rejected in AD 90, he sent his forces to Wakhan (Afghanistan) to attack Ban Chao. The conflict ended with the Kushans withdrawing because of lack of supplies. In AD 91, the office of Protector General of the Western Regions was reinstated when it was bestowed on Ban Chao.
Try to answer this question if possible (otherwise reply "unanswerable"): Who was the Protector General of the Western Regions in AD 91?
Ban Chao