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 Korean alphabet was designed so that people with little education could learn to read and write. A popular saying about the alphabet is, "A wise man can acquaint himself with them before the morning is over; even a stupid man can learn them in the space of ten days."
The project was completed in late December 1443 or January 1444, and described in 1446 in a document titled "Hunminjeong'eum" ("The Proper Sounds for the Education of the People"), after which the alphabet itself was originally named. The publication date of the "Hunminjeongeum", October 9, became Hangul Day in South Korea. Its North Korean equivalent, Chosŏn'gŭl Day, is on January 15.