Sejong the Great
Before the creation of Hangul, people in Korea (known as Joseon at the time) primarily wrote using Classical Chinese alongside phonetic writing systems based on Chinese script that predated Hangul by hundreds of years, including idu, hyangchal, gugyeol, and gakpil. However, due to the fundamental differences between the Korean and Chinese languages, and the large number of characters that needed to be learned, there was much difficulty in learning how to write using Chinese characters for the lower classes, who often lacked the privilege of education. To assuage this problem, King Sejong created the unique alphabet known as Hangul to promote literacy among the common people. His intention was to establish a cultural identity for Korea through its unique script.
Sin Sukju
Shin was an accomplished polyglot, and was particularly well educated in the Chinese language. He served as a personal linguistic expert to King Sejong, and was intimately involved in the creation and application of the Korean alphabet known in modern times as Hangul. Sin used the newly created hangul system to create an accurate transcription of spoken Mandarin Chinese in 15th century Ming dynasty China.
These transcriptions haven proven accurate and reliable, and his transcriptions are now "an invaluable source of information on the pronunciations of Ming-era [Mandarin]."