Korg was controlled by Yamaha in a short period of time between 1987 and 1993 but has been independent since then. Read the complete story of Korg here (highly recommended for all Korg fans):
http://www.soundonsound.com/sos/Oct02/articles/korg40th.asp http://www.soundonsound.com/sos/Nov02/articles/korganniversary2.asp http://www.soundonsound.com/sos/Dec02/articles/korganniversary.asp

Kind regards,
Tommy