Simon Marcus (born 5 November 1986), also known as The One, is a Canadian Muay Thai kickboxer of Jamaican descent, who competes in the light heavyweight and cruiserweight divisions.
Marcus took up Muay Thai at sixteen and achieved success as an amateur initially by medaling at three international tournaments as well as capturing the North American Cruiserweight Championship.
Having turned professional in 2009, he had a breakout year in 2012 when he beat Kaoklai Kaennorsing for the WPMF World Light Heavyweight title and defeated Joe Schilling twice in a notable rivalry.
As of 1 November 2018, he is ranked the #2 middleweight in the world by Combat Press.