For 10 points, name this great Korean king of Joseon whose reign saw the invention of Hangul.
This monarch's reign saw the publication and widespread distribution of the agricultural manual called the Straight Talk on Farming. This monarch granted the Sō family trading privileges in the Kakitsu Treaty, after the Ōei Invasion, a raid on pirate bases on Tsushima, took place during his reign. It was said that an innovation from this monarch's reign could be learnt by wise men in a morning and by stupid men in ten days. This monarch patronized the Hall of (*) Worthies, a group of scholars that wrote the manual known as the Hunmin Jeongeum ("hoon-meen jung-um") in order to promulgate a new alphabetic writing system that could be used by commoners in place of Chinese characters. For 10 points, name this great Korean king of Joseon whose reign saw the invention of Hangul.
This monarch's reign saw the publication and widespread distribution of the agricultural manual called the Straight Talk on Farming.
Sejong the Great [accept Yi Do or Lee To]