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.
Yeomillak
Yeominrak, which means "Enjoyment with the People", was created based on Korean court music that the king shared to his people to be enjoyed together. This song was created during his 29th year of reign (1447) and actually had lyrics from the Yongbi eocheonga, but only the melodic component is existent today. It is usually played on Hangul Day in South Korea to celebrate the promulgation of Hangul by King Sejong, and also in religious services for the Ancestral Shrine of the Royal family, honoring the Royal Court, and for the Civil and Military authorities.