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 the Joseon dynasty
During the rule of Sejong, Korea saw technological advances in natural science, agriculture, literature, and traditional medicine. Because of his success, Sejong received the title "King Sejong the Great of Joseon". His most remembered contribution is the creation of Hangul, the Korean alphabet, in 1443. Before that, Korean literati had used the Hanja writing system—traditional Chinese characters with Korean pronunciation and meaning—and a written language known as Hanmun, which was basically Classical Chinese, for official court documents. Everyday written use of Hanja and Hanmun ended gradually in the latter half of the 20th century.