Wikipedia
Daejongism ( Daejonggyo or Taejongkyo, "religion of the Divine Progenitor" or "great ancestral religion") or Dangunism ( Dangungyo or Tangunkyo, "religion of Dangun") is the name of a number of religious movements within the framework of Korean shamanism, focused on the worship of Dangun (or Tangun). There are around seventeen of these groups, the main one of which was founded in Seoul in 1909 by Na Cheol ( 나철, 1864-1916).
Dangunists believe their mythos to be the authentic Korean native religion, that was already around as Gosindo (古神道, "way of the Ancestral God" or "ancient way of God") at the time of the first Mongol invasions of Korea, and that was revived as "Daejongism" (Daejonggyo) just at the start of the Japanese occupation. The religion was suppressed during the Japanese rule.
The god of the religion is the legendary king Dangun, who ruled over a Korean empire around 5000 years ago. Its main tenet is that the Koreans have their own God and they have no need to worship foreign gods. Its emphasis is on the national identity and unity of the Korean people (known as minjok) and as such has been associated with Korean nationalism (and sometimes ultranationalism).
Daejongism does not focus so much on institutions or rituals but rather on central doctrines and associated mythologies, so that it is more definable as a creed or a faith system rather than an organized religion. A 1995 census found that fewer than 10,000 Koreans claim to follow the religion.