Yes, it's a holiday in South Korea because of this revered monarch, whose silhouette is perhaps one of the two most recognizable silhouettes downtown.
But there's a huge reason why King Sejong sits in the middle of Gwanghwamun Square bathing in reverence and tourist photography every day and night. King Sejong, or Sejong, The Great, promulgated the use of hangeul, or the Korean language.
If you're a foreigner living in Korea, a basic knowledge of the Korean language would be a big help in one's daily living. That's why I enrolled in a few Korean classes in my early years in Seoul, which made my buying bananas and, depending on the season, strawberries, persimmons and apples, from the fruit vendor down the street so much easier. And a few times, at E-Mart, too.
Hangeul is actually very easy to learn. King Sejong made sure of that. He and his scholars invented it in 1443 for illiterate people. And in the 21st century, one of these people, illiterate in hangeul that is, sat down in Korean classes and added a few more Korean words into his vocabulary.
So, thanks to the most photographed Korean monarch for making hangeul very easy. And for making this day a holiday.
And if you're in Gwanghwamun Square today, make sure you thank his highness, literally and figuratively, too.