양상국 (梁相國, 梁相国)
Also Sangguk, Sangkook, with or without spacing or hyphenation.
He qualified as a professional in 1970, was promoted to 8p in 1997 and to 9p on 2006-08-09.
Much more information is available about him in Korean, at the KBA and Korean Wikipedia outlinks.
KBA Ko. Wiki U-Go Waltheri Go4Go Go Ratings
Yang was noted for playing an unusual opening, with a 3-5 6-4 enclosure, against Cho Hunhyeon in 1975. You can read more about it on the Carrollian developments page.