Ch'oe Sejin (; ; 1465 – February 10, 1542) was a Korean linguist and a translator and interpreter of the Chinese language during the Joseon Dynasty. He is of the Goesan Choe clan and his courtesy name was Gongseo (). He is widely known for his research with the Korean hangul letters, and comparative studies with Chinese and Korean, which further led to the propagation of hangul during a time period when Chinese characters were used as the main system of writing. Ch'oe was recognized by many for his talents as an official interpreter in the Korean Embassies in Beijing and in his works in hangul research. However, he lived a tumultuous life due to this middle class status, which led him to be the target of many envious aristocrats of his era.
Ch'oe devised the modern Korean order of the hangul characters, and assigned names to the letters. His most famous book on hangul is the Hunmong chahoe ("Collection of Characters for Training the Unenlightened", 1527). Ch'oe Sejin's birth year is not found in any records, but given the record found in "", his birth year is estimated as 1465. However, there are other claims that he was born in 1473.
Ch'oe was known as very skilled as a translator and interpreter. However, during a time period when society was strictly stratified, his middle class status restricted his career and even led him to many difficulties and hardships. The noble class organized society in a way that they controlled and possessed a majority of the wealth and property of the country, and it was common for the nobility to be jealous over highly talented middle class government officials who might successfully become promoted, and surpass nobles in rank, although this was very rare. Ch'oe Sejin was a target for the nobles' jealousy, and he was sacrificed in the factional strife and tumultuous political climate at the time. For example, two months after he passed the "Bong Se Ja Byul Shi" Exam, his acceptance became nullified because of an involvement in a trial for the murder of the deposed Queen, Yoon. Even though he was not directly involved, the Minister of Culture and Education, Lee Sejwa, who conducted the exam and personally recommended Ch'oe was involved in the trial, and as a result, all acceptances were nullified. Some were able to retain their acceptance due to familial ties, however, Ch'oe was not one of them. Even after 3 years of waiting, he was accused of writing the anonymous letter criticizing the National Court in 1507 and was subject to a severe sentence. He was saved from this accusation after more investigation, but this highlights the kind of difficulties he faced due to his social class. Ch'oe also ordered the vowels in Hangul. He ordered them according to sequence in which we open our mouth to articulate these vowels. His ordering of the vowels is the order that is currently used in present-day Korea.
Hunmong chahoe has been republished 10 times over the time period of 400 years.
- Sohak p'yŏnmong (; 1537) is a textbook for Chinese language learners, dedicated to the King.
- Unhoe okp'yŏn (; 1537) is a supplementary material published to add on to the works in Sasung Tonghae.
- Yŏhyogyŏng (; 1541) was one of his last works, written when he was 76.