Tomoyuki Oka, better known by his ring name Great-O-Khan, is a Japanese professional wrestler signed to New Japan Pro-Wrestling (NJPW), where he is a member of the United Empire stable. He also wrestles for NJPW's United Kingdom based partner promotion Revolution Pro Wrestling (RevPro), where he is the former Undisputed British Heavyweight Champion. In NJPW, he is a two-time IWGP Tag Team Champion (with Jeff Cobb).