Simon Lessing, MBE, (born 12 February 1971) is a British triathlete who won five International Triathlon Union (ITU) world titles (1992, 1995, 1996 and 1998). He also won races at ITU long distance and Ironman-distance events. In 2008 he retired from professional racing, and now resides in Boulder, Colorado, United States.

In the first 25 years of International Triathlon Union events, some athletes might have competed in more races, but none had more success than Simon Lessing. As the only athlete to capture four ITU World Championship titles, as well as two silver medals and one bronze, Lessing has been the most consistent performer on race days.

Born in Cape Town, South Africa, his father and mother (who was a swim coach) supported him. By the end of his fifth year at school, he had won honours in swimming, sailing and biathlon and was known as a cross-country runner. In 1988 Lessing was South African national champion, but after he finished high school he wanted to compete internationally, he made the decision to represent Great Britain, his mother’s home nation. At the time South Africa was banned from competing in all international sporting competitions due to Apartheid.

He quickly made an impact in the sport and finished 7th in his first ITU World Championship race in Orlando, in 1990. In 1991, he finished 6th, before capturing his first ITU World Championship title in 1992. While Spencer Smith won in 1993, Lessing returned in 1995 and captured his third and fourth titles in 1995 and 1996. In 1997 he finished third, before returning to his best in 1998 – to collect his fourth ITU World Championship title. In 1999, his last ITU World Championship race, he was leading with less than 500m to go when Dmitriy Gaag rolled past, relegating him to silver.