My mother's last name is Son and her immediate family lives in Kyeungju, Korea. I don't know which sub-clan she comes from. What is the folklore around the "very first" Son?
Because the Korean already wrote a lot on Korean last names, often the Korean would receive questions regarding specific last names such as yours. So far the Korean has been answering them privately, but it would be interesting to build an archive of Korean last name-related stories. So here it goes.
The Korean assumes that you meant to spell "Gyeongju", a city in southeastern Korea which has a great historical heritage. Although it is entirely possible that your mother is not Gyeongju Son (pronounced sohn,) it is fairly likely. Therefore, the Korean will provide the story for the first Gyeongju Son.
Gyeongju Son clan has an interesting story. Originally, the last name began when in 32 AD, the king of Shilla (one of the three kingdoms in the Korean peninsula at the time) gave the last name Son to one of the tribe leaders. At the time, the kingdom of Shilla was essentially a federation of six tribal villages, so giving a gift as lavish as a last name was a good idea for a king who must please the village leaders.
However, currently Gyeongju Son clan considers a person named Son Sun (Sohn Soon) to be the first Gyeongju Son. Son Sun was a poor man who lived with his elderly mother, wife, and a young child. The whole family barely had enough to eat, but the young child would always take Son Sun's mother's food. Seeing that, Son told his wife: "We can have another child, but we cannot have another mother. My mother must be starving because our child keeps on taking her food. We should bury the child so that my mother can eat well."
So the couple took the child into a nearby mountain and began digging a hole. But when they did, they found a strange bell made of stone. The couple hung the bell on a tree and tried ringing it, and the sound was beautiful and clear. The wife said "It must be the child's fortune to gain this strange object, so let us take the child back." Son Sun agreed, and took the child and the bell home. Son rang the bell, and the clear sound would travel all the way to the palace. The king asked about the sound of the bell, and the king's envoy learned the story and told the king. The king, moved by Son's filial piety, gave Son a house and a lot of food to honor his virtue. Son turned his previous house into a temple, and put the bell there.
Rather interesting story because it shows how seriously traditional Koreans regarded being good to your parents. Another interesting part is the surprising element of death and cruelty in the story, told in a matter-of-fact tone -- it is a familiar refrain in Korean folk tales.
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