許浚
Heo Jun is the son of a concubine and the governor of Yeongcheon. When he witnesses brilliant doctor Yoo Ui-tae save a dying person, he decides to become a doctor. First he works as a medicinal herb gatherer, then with the help of Ye-jin at Yoo Ui-tae's clinic, he studies rare medical texts imported from the Ming dynasty. With his expanded medical knowledge, Heo Jun begins to treat patients under Yoo Ui-tae's tutelage. But he later despairs of his inability to cure his mentor's stomach cancer. Despite the era's oppressive caste system and his commoner background, Heo Jun rises to the top of his field and becomes King Seonjo's royal physician.