Hanja
Although a phonetic Korean alphabet, now known as Chosŏn'gŭl or Hangul, had been created by Sejong the Great, it did not come into widespread official use until the late 19th and early 20th century. Thus, until that time it was necessary to be fluent in reading and writing Hanja in order to be literate in Korean, as the vast majority of Korean literature and most other Korean documents were written in Literary Chinese, using Hanja as its primary script. Today, a good working knowledge of Chinese characters is still important for anyone who wishes to study older texts (up to about the 1990s), or anyone who wishes to read scholarly texts in the humanities. Learning a certain number of Hanja is very helpful for understanding the etymology of Sino-Korean words, and for enlarging one's Korean vocabulary. Today, Hanja are not used to write native Korean words, which are always rendered in Hangul, and even words of Chinese origin—"Hanja-eo" ()—are written with the Hangul alphabet most of the time, with the corresponding Chinese character often written next to it in order to prevent confusion with other characters or words with the same phonetics.
Origin of Hangul
Following the Indic tradition, consonants in the Korean alphabet are classified according to the speech organs involved in their production. However, the Korean alphabet goes a step further, in that the shapes of the letters iconically represent the speech organs, so that all consonants of the same articulation are based on the same shape. That is, the Korean alphabet is a featural alphabet, the only one in the world that is in common use. For example, the shape of the velar consonant (牙音 "molar sound") ㄱ is said to represent the back of the tongue bunched up to block the back of the mouth near the molars. Aspirate ㅋ is derived from this by the addition of a stroke which represents aspiration. Chinese voiced/"muddy" ㄲ is created by doubling ㄱ. (The doubled letters were only used for Chinese, as Korean had not yet developed its series of emphatic consonants. In the twentieth century they were revived for the Korean emphatics.)