Origin of Hangul
Ledyard holds that the Koreans adopted five core consonant letters from ’Phags-pa, namely ㄱ "g" , ㄷ "d" , ㅂ "b" , ㅈ "j" , and ㄹ "l" . These were the consonants basic to Chinese phonology, rather than the graphically simplest letters (ㄱ "g" , ㄴ "n" , ㅁ "m" , and ㅅ "s" ) taken as the starting point by the "Haerye." A sixth letter, the null initial ㅇ, was invented by Sejong. The rest of the consonants were developed through featural derivation from these six, essentially as described in the "Haerye"; a resemblance to speech organs was an additional motivating factor in selecting the shapes of both the basic letters and their derivatives.
History of Korea
During the 15th and 16th centuries, Joseon enjoyed many benevolent rulers who promoted education and science. Most notable among them was Sejong the Great (r. 1418–50), who personally created and promulgated Hangul, the Korean alphabet. This golden age saw great cultural and scientific advancements, including in printing, meteorological observation, astronomy, calendar science, ceramics, military technology, geography, cartography, medicine, and agricultural technology, some of which were unrivaled elsewhere.