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 "Hunmin Jeong-eum" states that King Sejong adapted the ("gojeon", ""Gǔ" Seal Script") in creating the Korean alphabet. The has never been identified. The primary meaning of "gǔ" is "old" ("Old Seal Script"), frustrating philologists because the Korean alphabet bears no functional similarity to Chinese "zhuànzì" seal scripts. However, Ledyard believes "gǔ" may be a pun on "Měnggǔ" "Mongol", and that is an abbreviation of "Mongol Seal Script", that is, the formal variant of the 'Phags-pa alphabet written to look like the Chinese seal script. There were 'Phags-pa manuscripts in the Korean palace library, including some in the seal-script form, and several of Sejong's ministers knew the script well.