During his reign the power of the Buddhist heirarchy was reduced and a system for recording the Korean language phonetically was introduced.
Citation:
Editors. "Korean cultural efflorescence under the reign of Sejong".
The Literary Encyclopedia. First published 01 March 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=9643, accessed 19 May 2013.]