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.

New Japan Pro-Wrestling (NJPW) is a Japanese professional wrestling promotion founded on January 13, 1972, by Antonio Inoki, and based in Nakano, Tokyo. It is currently owned by card game company Bushiroad, while TV Asahi and Amuse, Inc. own minority shares of the company. Naoki Sugabayashi has served as the promotion's Chairman since September 2013, while Hiroshi Tanahashi has served as the president of the promotion since December 2023.