The Tong Yang Securities Cup was a annual tournament sponsored by Tong Yang Securities (which now seems to have been renamed Tong Yang Investment Bank).
The 1st Tong Yang Cup was a purely Korean tournament, but for the 2nd event some Chinese players were invited as well. From the 3rd event onwards the tournament became a fully fledged world go championship. This third event was won by Yi Ch'ang-ho. It was his first international title, and can be considered to mark the beginning of Korean domination of world go.
Winners and defeated finalists:
1st 1990 Yang Chae-ho 3-1 Chang Soohyun (*) 2nd 1991 Seo Pong-su 3-1 Yi Ch'ang-ho 3rd 1992 Yi Ch'ang-ho 3-2 Rin Kaiho 4th 1993 Yi Ch'ang-ho 3-0 Cho Chikun 5th 1994 Cho Hun-hyeon 3-1 Yoda Norimoto 6th 1995 Ma Xiaochun 3-1 Nie Weiping 7th 1996 Yi Ch'ang-ho 3-1 Ma Xiaochun 8th 1997 Cho Hun-hyeon 3-0 Kobayashi Satoru 9th 1998 Yi Ch'ang-ho 3-1 Yu Ch'ang-hyeok
(*) All sources I could find give this name, but there appears to be no such player. It may mean Cheong Su-hyeon.