Hanja are Chinese characters borrowed from and incorporated into the Korean language and given uniquely Korean pronunciations. Unlike the Japanese equivalent, called kanji, most hanja have not been simplified and remain identical to the traditional Chinese characters. Until the late 19th and early 20th centuries, fluency in this writing system was necessary to read and write Korean. This writing system based on Chinese characters then yielded to a phonetic Korean alphabet system called hangul that was created in the 1440s but not widely implemented for centuries.
The Korean writing system was once based on Chinese characters. It is believed that the use of these characters was necessitated by the introduction of Buddhism. The sixth-century Chinese poem titled the Thousand Character Classic, a primer for teaching Chinese characters, also gained popularity in Korea and influenced the development of hanja. By 1583, the poem was being used as a writing primer as well. As Korea did not have its own writing system until the 1440s, the Chinese characters were used instead.
Properly literate Koreans thus had to master hanja. Each character is formed using one of 214 radicals, plus additional elements that indicate sound, although a few are pictographic. The meaning of these borrowed Chinese characters generally remained the same throughout China, Japan, and Korea, although the pronunciation of each character became uniquely Korean over time.
In the 1440s, King Sejong the Great and his scholars developed a phonetic Korean script now known as hangul that competed with the logographic hanja. The promotion of hangul was spurred by the fact that the Chinese characters were difficult for most people to master, resulting in a large portion of the population that was illiterate. Hangul was supposed to be easier to learn, and it became part of popular culture despite opposition from the literary elite. It did not fully supplant hanja until the 20th century.
Hangul is the official written language of both North and South Korea, having been used in official documents since 1894. The old system has never disappeared entirely, however. Hanja were banned in North Korea by Kim Il Sung but reintroduced in 1964 for reasons that are not entirely clear. Students in North Korean elementary and high school learn approximately 2,000 characters.
South Korea has alternatively banned and reintroduced these Chinese characters throughout the 20th century. A definitive ban was issued in 1955, but the old system was back by 1964, with more than 1,300 hanja in school textbooks. All school texts were written in hangul by 1970, but middle and high school students continue to be taught around 1,800 hanja as a separate course. Graduate students in Korean language and studies programs are also usually required to master these basic Chinese characters.
Fluency remains necessary for historians and other scholars who study Korean historical documents or literature that predates the introduction of hangul. Children are taught some of the old writing system in school, but there is little opportunity to practice reading these characters in daily life. Hangul is now used for native Korean words and even most words native to Chinese. Most hanja continue to appear primarily in personal names and some university textbooks, often with the hangul equivalent.