The story of Phra Ruang appeared in many books written from the late Ayutthaya period with different contents but a similar storyline. The story was that one king went out into the forest to practice Buddhist teaching. He met beautiful Naga and fell in love with the course and Naga was pregnant. Then, the king wished to return to the city and Naga thought that she was abandoned, then she left the egg and went back to the underwater world. The egg became a beautiful boy. An old man and an old woman brought him with love and called him "Ruang", with a miracle "supernatural words".

Some of the stories of Phra Ruang provided different details, such as in Chulayuth Karn Wong, it was said that Naga vomited her blood and a toad swallowed it, but it could not bear the poison, so it finally died. Phra Ruang lived in the toad and asked to stay with an old man and an old woman. When the old man and the old woman went out to do farming. He came out from the toad and became a beautiful boy, taking care of the house and preparing meals for the man and the woman. Then, when they knew a secret, they burned the toad. The Chiang Mai Chronicle said that the mother of Phra Ruang was a butterfly giant (a giant with a duty to preserve the place) falling in love with a hunter, "she got him and the called Phraya Ruang".

However, if it was a story from the people in the Sukhothai area, they would point out that it happened at Khao Luang (Ramkhamhaeng National Park), the place where Phra Ruang's mother and father met. There was a crater of Naga with a deep hole believed to be a route connecting the human world with the underwater world. There was a cave named "Maherok" believed to be from the word "afterbirth was not seen" because it was a cave where Naga left her egg and it became Phra Ruang. The old man and the old woman found him but did not see his afterbirth. That was the name of the cave.