The story behind National Foundation Day is one of the strangest of any public holiday of any sovereign nation that I know. The most authoritative site I found is the Visit Korea website, which tells it like this:
“The Dangun legend is a mythical story that portrays the origin of the Korean people as descendants of bear, and the founding of Korea through Dangun. As legend has it, a tiger and bear prayed to Hwanung, the son of the Lord of heaven, to become human. Upon hearing their prayers, Hwanung gave them 20 cloves of garlic and a bundle of mugwort each, ordering them to eat only this sacred food and remain out of the sunlight for 100 days.
The tiger gave up after about twenty days and left the cave. However, the bear remained and was transformed into a woman. The bear-woman married Hwanung, and soon gave birth to a son, who was named Dangun Wanggeom. Dangun built the state of Gojoseon. Korea honors the day of establishing the first state through the national holiday of *Gaecheonjeol* (National Foundation Day) on October 3rd. On the first day of the lunar year, a group gathers for a memorial service for Dangun at a Chamseongdan Alter (stone structure known to be built by Dangun) located on holy mountains, including Manisan Mountain on Ganghwa Island and Taebaeksan Mountain in Gangwon-do.
Koreans accept and interpret the Dangun legend to be more than a mythical story. Just as the story of the Fall of Troy had been accepted by the world as a vague mythical story until remains were discovered, Koreans believe that the Dangun legend could be a trace of the foundation story of the first ancient kingdom on the Korean peninsula. Based on the Dangun legend, Korean historians date the origin of Korea’s legitimate history back to some 50,000 years ago.”
The date was originally the 3rd day of the 10th month of the lunar calendar, and despite the website’s reference to 50,000 years, the official date of the Dangun story is 2333 BC. Certainly, archeological evidence of human occupation of Korea dates to 10,000 BC.
In 2006 (the first year of my first stay here), I expressed great skepticism about this story in my blog of the time, but there may be more to it than meets the eye. On Wednesday and Thursday, after the Chuseok long weekend, I asked my second-year classes to tell me about various Korean holidays, including this one. The best student in one class said (and I paraphrase) that the tiger and bear may represent clans or tribes of pre-historic Korea, and the ‘son of the Lord of heaven’ a group from what is now China or Russia, possessing comparatively advanced culture and technology. The ‘bear clan’ accepted and merged with the new group and together they formed the society which became distinctively Korean.
None of websites I found mention anything about this, so I can’t say yes or no to what he said. Most of the sites associated with the Dangun story are now in the DPRK, which the government there uses to support its claim to sovereignty over the whole peninsula, and to make generally unsubstantiated claims, including identifying his burial site. The Wikipedia article rather mildly states: ‘Many observers and historians outside of North Korea, including South Korea, consider the data and the interpretation compromised by politics and nationalism.’