When the egg hatched a young boy, Chumong, emerged. After only one month he began to speak. He complained to his mother that he couldn't sleep because of the flies that were biting his eyes. He asked that she make him a bow and arrow, and she did so. Chumong took the bow, and with every arrow he shot he hit a fly.
Chumong's skill improved as he became a young man. He often went hunting with the king's seven sons, and although they might catch one deer all together, Chumong would catch many. The eldest prince warned his father, "Chumong is a boy of supernatural powers--it would be best to take care of him quickly before he grows to be a man." So the king ordered Chumong to work as a stable boy, to see how he would react to being ordered to do such lowly work.
Dissatisfied with such a lowly station, Chumong said to his mother: "I am the son of a god--this is no way for me to live. I will go to the south and found a nation of my own." His mother answered, "I, too, have worried about this day and night. Since you will be traveling such a long way, let me choose a good horse for you." His mother went to the corral and snapped a large whip, frightening all the horses. One of the horses leaped over a fence the height of two men. Chumong saw this and knew immediately that this was an exceptional horse. Secretly he stuck a needle in the horse's tongue so that he wouldn't be able to eat or drink.
When the king saw that all the horses had become big and strong he was very happy, and he gave the thin, starving horse to Chumong. Chumong took the needle from the horse's tongue and fed him very well. When the horse was healthy he fled south until he came to a great river. The king's troops were fast on his heels, so he pointed his whip at heaven and shouted, "I am the son of Haemosu, the son-in-law of Habaek, and I have thus far escaped disaster. Now may the gods of heaven and earth have mercy on me and send a bridge." Then he struck the water with an arrow, and all the fish and turtles in the river came up to the surface and formed a bridge. Chumong quickly rode across, even as the king's troops were approaching. When he had reached the other side, the fish and turtles dove back into the water, and all the king's men that were on the bridge drowned.
When he had parted with his mother she had given him many different seeds of grain, but somewhere along his journey he had lost the barley seed. As he was resting beneath a great tree, a pigeon came flying into view. He thought to himself, "Since I have lost the barley seed, my heavenly mother has sent me another." He shot an arrow and killed the pigeon, and when he opened up its throat he found a barley seed there. Then he put the pigeon into the water and it came to life and flew away again. He decided to found his nation at that place, and he gathered vassals around him and declared himself king.
One day, when he was out hunting, he met Songyang, the original king of the land. When Songyang asked him who he was, Chumong answered, "I am a descendant of the god of heaven, and I am now king of this land." Songyang replied, "I have been king of this land for some time now, so don't you think it would be right for you to submit to me?" Chumong said to him, "You are no descendant of the gods, so if you do not submit to me heaven will surely strike you down."
Songyang decided to try another tactic. "The mark of a great king is surely his skill in archery," he said. "Let us have a contest." He commanded one of his servants to draw a deer and place it at a hundred paces. Songyang took aim and fired, but he missed his target. Then Chumong commanded his servant to place a jade ring at a hundred paces, and he broke it with one arrow.
Songyang was defeated, and Chumong commanded rain to fall from heaven. It rained for seven days, and Songyang's capital was swept away in a flood. With the help of heaven, Chumong erected his own palace in another seven days, and thus he founded the kingdom of Koguryeo.