Wang San-ak (왕산악, 王山岳, ?-?) was the Prime Minister of Goguryeo during the reign of King Yangwon.
According to the Samguk Sagi, written in 1145, the geomungo was invented by him by using the form of the ancient Chinese instrument guqin (also called chilhyeongeum, literally "seven-string zither"). After his death, the instrument was passed down to Ok Bogo, Son Myeong-deuk, Gwi Geum, An Jang, Cheong Jang, and Geuk Jong, while being widely spread over the kingdom.
References
Wang San-ak Wikipedia(Text) CC BY-SA