Who they were
He was born c. 1390 in Dongnae as a government slave (nobi). King Sejong recognized his talent, had him freed, and promoted him to court office over objections — a famous story of talent overcoming caste.
What they did
The works associated with him include the automatic striking water clock Jagyeongnu (1434), armillary spheres and other celestial instruments, and sundials — part of the court program that also produced the standardized rain gauge in 1441. In 1442 a royal palanquin built under his supervision broke; he was punished and disappears from the records, and his death date is unknown.
Legacy
He is Korea’s emblematic inventor. His name marks science prizes and institutions, and his rise from slavery is part of the luster of the Sejong era.