Hangul Day
Before the creation of Hangul, people in Korea (known as Joseon at the time) primarily wrote using Classical Chinese alongside native phonetic writing systems that predate Hangul by hundreds of years, including idu, hyangchal, gugyeol, and gakpil. However, due to the fundamental differences between the Korean and Chinese languages, and the large number of characters needed to be learned, there was much difficulty in learning how to write using Chinese characters for the lower classes, who often didn't have the privilege of education. To assuage this problem, King Sejong created the unique alphabet known as Hangul to promote literacy among the common people.
Origin of Hangul
In order to maintain the Chinese convention of initial and final, Sejong and his ministers needed a null symbol to refer to the lack of a consonant with an initial vowel. He chose the circle, ㅇ, with the subsequent derivation of the glottal stop ㆆ "’" , by adding a vertical top stroke by analogy with the other stops, and the aspirate ㅎ "h" , parallel the account in the "Haerye." (Perhaps the reason he created a new letter rather than adopting one from ’Phags-pa was that it was awkward to write these Chinese initials in ’Phags-pa, where ㅇ and ㆆ were both written as digraphs beginning with "y," ꡭꡝ and ꡗꡖ.) However, Ledyard's explanation of the letter ㆁ "ng" differs from the "Haerye" account; he sees it as a fusion of velar ㄱ "g" and null ㅇ, reflecting its variable pronunciation. The Korean alphabet was designed not just to write Korean, but to accurately represent Chinese. Many Chinese words historically began with , but by Sejong's day this had been lost in many regions of China, and was silent when these words were borrowed into Korean, so that only remained at the middle and end of Korean words. The expected shape of a velar nasal, the short vertical stroke (⃓) that would be left by removing the top stroke of ㄱ "g", had the additional problem that it would have looked almost identical to the vowel ㅣ "i" . Sejong's solution solved both problems: The vertical stroke left from ㄱ "g" was added to the null symbol ㅇ to create ㆁ "ng", iconically capturing both regional pronunciations as well as being easily legible. Eventually the graphic distinction between the two silent initials ㅇ and ㆁ was lost, as they never contrasted in Korean words.