Gwanghaegun appreciated Heo’s talent and loyalty. In 1610, Heo finally completed the twenty-five volumes of Donguibogam after fifteen years of continuous effort. He spent the last years of his life educating young physicians of Naeuiwon until he died in 1615. The title of senior first rank officer was conferred posthumously—an unprecedented feat that had long been hampered by yangban officials. He wrote several medical texts, but his most significant achievement is Donguibogam. Donguibogam means “Mirror of Eastern Medicine”, which is often noted as the defining text of traditional Korean medicine. The work spread to East Asian countries like China, Japan, and Vietnam where it is still regarded as one of the classics of Oriental medicine today. It is divided into five chapters: Internal Medicine, External Medicine, Miscellaneous Diseases, Remedies, and Acupuncture. In the first chapter, Internal Medicine, Heo describes the interdependence of the liver, lung, kidney, heart, and spleen. The chapter on External Medicine explains how the skin, muscles, blood vessels, tendons, and bones allow for movement and maintenance of posture. The chapter on Miscellaneous Diseases describes various diseases' symptoms, diagnoses, and treatment methods. Heo’s remedies rely on medicinal herbs and plants, and he provides impressively detailed instructions on how to extract, maintain, and consume the herbs. The last chapter explicates acupuncture strategies. Donguibogam is one of the most valued treasures of Korea owing to its originality and quality. It provides valuable medical knowledge and also reflects the philosophy of seventeenth-century East Asia. Although Heo Jun worked extensively with the royal family, he emphasized making treatment methods accessible and comprehensible to common people. Whereas common medical practice was to elevate the perceived value of treatment by using rare and expensive ingredients, he instead found natural herb remedies that were easily attainable by commoners in Korea and that was just as effective. Furthermore, he wrote the names of the herbs using the simple hangul letters instead of using more difficult hanja (Chinese characters), which most commoners did not understand. As the backbone of Eastern medicine to this day, Donguibogam was recently included in UNESCO’s Memory of the World Register in 2009. To this day, Heo Jun is revered as a brilliant physician and a loyal and compassionate person, who strived to develop accessible treatments for the poor and uneducated citizens. Heo Jun's name and accomplishments are widely recognized by Koreans even today. Korean people still refer to Heo Jun's natural remedies