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.
Hall of Worthies
The Hall participated in various scholarly endeavors, of which the best-known may be the compilation of the "Hunminjeongeum", in which the hangul writing system was first formulated. In the Hunminjeongeum, King Sejong wrote a preface which explained the origin and purpose of the newly created alphabet, Hangul. He then instructed his scholars of the Jiphyeonjeon (Hall of Worthies) to write detailed explanations of each of its letters along with examples of each of them. The purpose of the Hunminjeongeum was to provide instructions on how to use the new alphabet. The definitive edition of the Hunminjeongeum is known as the Haerye Edition of Hunminjeongeum (Haerye refers to the explanations and examples of the Hall of Worthies scholars, which were previously missing in other known editions)