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.
Hangul
The Hangul Society, founded by Ju Si-gyeong, announced a proposal for a new, strongly morphophonemic orthography in 1933, which became the prototype of the contemporary orthographies in both North and South Korea. After Korea was divided, the North and South revised orthographies separately. The guiding text for orthography of the Korean alphabet is called "Hangeul Matchumbeop", whose last South Korean revision was published in 1988 by the Ministry of Education.