This is the second form taught in the Ch'ang Hon Hyung series. It is called Tan-Gun Hyung or Tan-Gun Tul in modern ITF and ITF-derived schools. In his 1965 book on Taekwondo, Choi Hong Hi writes this on Tan-Gun Hyung: "Tan-Gun is named after the holy Tan-Gun, the legendary founder of Korea in the year of 2334 B.C." And that is really all the background you get on this character. I only recently learned this form in my exploration and re-connection with my Oh Do Kwan roots (I have one teacher with Ji Do Kwan roots and one with Oh Do Kwan roots), but I was taught the story of Tan-Gun early on in my Taekwondo study. There are different versions but here follows the story as I was taught by my teacher:
"Once upon a time, a long long time ago, the Creator of Heaven and Earth got a son. The child grew up to be a handsome young man who was proned to be bored. When he got bored he searched out and amused himself by observing the wild animals. One time he chose a tiger and a bear and decided to put them to a test, but he also promised that if they passed they would become human. The test was that they would live in complete darkness in twenty days. The Tiger quickly became restless and left, but the Bear was patient and stuck to it for all 20 days. When the trial was over the Bear became a beutiful woman. She was so beutiful in fact that the Creators son layed with her, and together they got a son who they called Tan-Gun. He became a human and lived among humans and he founded the earliest Korean dynasty and society. "
As I said there are multiple different versions, but the gist of it remains the same. Tan-Gun is said to have established the earliest laws as well as religion as he is said to have made the first alter at Mari San, and it is also said he ruled with wisdom for twelve hundred years.
The form itself is interesting as it really focuses on high section punches. One reason for the focus on high section punches is suposedly to symbolise Tan-Gun climbing a mountain. As the Kukki Taekwondo Poomsae deliver 90% of all punches to the midsection I find it very refreshing to keep all punches high :-) below you can see me trying to do the form