In the old books it says (King) Mugang, but this is a mistake. There was no King Mugang in Paekche.
The name of the thirtieth ruler, King Mu, was Chang. His mother was a widow. She had built a house near a pond south of the capital. She had relations with the dragon of the pond, and gave birth to a son. His name was Sŏdong. His skills and talents were so many, it is impossible to count them. Probably because he made his living cultivating and selling yams, the people of that region called him Yam Boy, Sŏdong.
Hearing that Sŏnhwa, whose name is also written with the characters for beautification, the third daughter of King Chinp’yŏng of Silla, was a peerless beauty, Sŏdong cut his hair short and traveled to the Silla capital. There he gave the children of the region yams to eat, so they came to feel friendly toward him and follow him around. He then composed a song and taught them to sing it. The song was as follows:
Princess Sŏnhwa keeps
her secret love secret.
She goes at night to sleep
in the arms of her Sŏdong.
Before long, the song was heard everywhere in the capital. When the court officials reported this to the king, he ordered the princess into exile. Just as she was leaving, the queen gave her a quantity of gold for her travels.
As the princess was reaching the outskirts of town, Sŏdong appeared and, with a bow, announced that he wished to help her. For her part, though she had no real idea where he had come from, she quickly came to trust him. And so it was that as she went along with him, they formed a relationship. Afterward, when she learned his name at last, she realized the effects of the children’s song.
After they arrived in Paekche, she uncovered the gold her mother had given her, saying it would be useful for their livelihood. Sŏdong laughed at this, saying “What is this stuff, then?” The princess replied, “It is gold. This much will enable us to have a prosperous life.” “Since I was young,” came the reply, “I piled up lots of this stuff like dirt, when I was digging my yams.” Sŏnhwa, in astonishment, replied, “That is the most precious material under heaven. If you still know where it is, what would you think about sending an amount of it to my parents in the palace?”
Sŏdong agreed. He collected the gold, mounding it up like a hill. He asked the priest at Saja Temple what to do next. The priest replied, “Bring it to me. I can send it with my magical powers.”
Sŏnhwa wrote a letter and brought it with the gold to Saja Temple. In one night, the priest sent it all to the Silla palace. King Chinp’yŏng regarded all this as quite miraculous. Holding Sŏdong in ever higher regard, he sent letters daily with his regards and greetings. Sŏdong consequently rose in the esteem of the people, and soon became king.
One day, King Mu and his wife were on their way to Saja Temple. As they reached the shore of a pond at the base of Mount Yonghwa, Dragon-Gleaming Mountain, an image of the Maitreya, Mirŭk, appeared in the midst of the waters. They stopped and offered obeisance on the spot. The queen said to the king, “We must build a great temple here. This is my earnest wish.”
The king agreed. He went to the priest and asked about moving the pond. With his magical powers, in the space of one night the priest moved the pond and the mountain, and turned all into level ground. He fashioned a statue of the three-figured Maitreya. With the meditation hall, the pagoda, and the living quarters in their several places, the temple was named Mirŭk Temple. In the national history it is called Wanghŭng Temple, Temple of the King’s Pleasure. King Chinp’yŏng sent many different kinds of laborers to assist with the construction. The temple still stands today.
In the Three Kingdoms Chronicle, he (Sŏdong) is referred to as the son of King Pŏp, while here as a widowed woman’s son. There is no way to decide between the two accounts.