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.
Gari Ledyard
Although several of the basic concepts of hangul came from Indic phonology through the Phagspa script, such as the relationships among the homorganic consonants and, of course, the alphabetic principle itself, Chinese phonology also played a major role. Besides the grouping of letters into syllables, along the lines of Chinese characters, it was Chinese phonology, not Indic, that determined which five consonants were basic, and therefore to be retained from Phagspa. These were the tenuis (non-voiced, non-aspirated) plosives, "g" for ㄱ , "d" for ㄷ , and "b" for ㅂ , which were basic to Chinese theory, but which were voiced in the Indic languages and not considered basic; as well as the sibilant "s" for ㅈ and the liquid "l" for ㄹ . (Korean ㅈ was pronounced in the 15th century.)