---
node: jang_yeong_sil
type: person
slug: jang_yeong_sil
title: "Jang Yeong-sil"
lead: "Jang Yeong-sil (c. 1390–after 1442; his dates are uncertain) was the great inventor of King Sejong's court. Born a government slave, he was freed and promoted to office, and built the automatic striking water clock Jagyeongnu in 1434."
published: 2026-07-09
updated: 2026-07-09
image_file: jang_yeong_sil.jpg
image_source: "https://commons.wikimedia.org/wiki/File:Jang_Yeong-sil,_KAIST.jpg"
image_author: "AhmadElq"
image_license: "CC BY-SA 4.0"
---


## 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.