Han Geul(or Hangul) is Korean Letter system which is said to have been invented by King Sejong in Choseon Period. Those days, most Korean people and scholars were using Chinese letters to express what they thought. But the lingual system of Korean and Chinese were much different so that it was not easy to do it, especially when they were common people. And Chinese letters were ideograms, so it was difficult to learn to read and write them.

So King Sejong invented Hunmin Jeong eum, which implies "the right letters for teaching people."(or corrected sounds to teach people) This was the birth of Hangeul, the Korean letter system. He said explicitly that he made this letters since it was pity of people to borrow letters from another country to express what they want to say.

The system of Hangeul is very scientific and philosophical. The five basic consonants were modeled after the vocal organs, and adding a stroke or partially altering the shapes of the five basic consonants formed the rest. The vowels were made of compositions of Samjae(Sky, Earth, and Man). Then the whole system come to composed of scientific materials along the flow of philosophical composition. Actually, every phoneme contains at least one vowel with one or two consonants. (Refer to "Han-gul's unique scientific features" for some more detailed explanantion)