Heo Jun (허준, 1539 – 9 October 1615) was a Korean physician. He was the royal chief physician of Naeuiwon during the reign of King Seonjo and King Gwanghae of the Joseon Dynasty in Korea. Biography Heo Jun was born in 1539 to an affluent military family. He was well educated and financially secure throughout his childhood. Although he belonged to a wealthy and respected household, he is thought to have faced discrimination from his lineage members and other aristocrats because he was born to a concubine. During the Joseon Dynasty Korea, illegitimate children of aristocrats could not maintain their fathers’ yangban or noble status and instead, were considered chungins. Chungins, or “middle people,” typically referred to technicians and administrators subordinate to yangbans. While Heo’s motivation to pursue medicine is unclear, his social status as a chungin may have prevented him from becoming a civil or military officer like his father. He was appointed as a court physician at the age of 29. In 1571, at age 32, Heo entered Naeuiwon, the royal clinic of Joseon. After that, he was continuously promoted within the clinic at an unprecedented rate. In 1575 Heo treated King Seonjo, the fourteenth king of Joseon, and rose to senior third rank1 government official position after curing the Crown Prince’s smallpox in 1590. The Imjin War, further solidified King Seonjo’s trust in Heo, who loyally accompanied the King throughout the war in contrast to other government officers who cowardly fled to protect their own lives. King Seonjo rewarded Heo’s allegiance and yet another successful treatment of the diseased Crown Prince by promoting him to the senior second rank in 1596. In 1600, Heo became the chief physician of Naeuiwon. During this time, King Seonjo ordered Heo to write a medical book for his citizens, who suffered from epidemics and post-war famines. He wanted to publish a book that promoted preventative care and detailed drug formulas and treatment methods that even uneducated commoners could easily comprehend and access. King Seonjo’s initiative is noted as one of the first public healthcare programs of Joseon. In 1608 King Seonjo died. Government officials jealous of Heo’s illustrious career accused him of being culpable for the King’s death. Heo was exiled to the countryside Ulju, where he continued to write the book. In 1609, King Gwanghaegun, the successor to Seonjo, restored Heo to office despite many officials’ disapproval. Like his father,