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.
Joseon
During the rule of Sejong, Korea saw advances in natural science, agriculture, literature, traditional Chinese medicine, and engineering. Because of such success, Sejong was given the title "Sejong the Great". The most remembered contribution of King Sejong is the creation of Hangul, the Korean alphabet, in 1443; everyday use of Hanja in writing eventually was surpassed by Hangul in the later half of the 20th century.