He was South Africa 100 km Champion in 1991. He represented South Africa at the IAU 100 km World Championships in 1993, 1994 & 1995.[4] He is popular for his Comrades Marathon win in 1992. He was disqualified for taking over the counter cold medication, containing, phenylpropanolamine. It was a prohibited stimulant, but was removed from the banned list shortly after the disqualification. Phenylpropanolamine is not one of the prohibited stimulants the World Anti-Doping Agency listed on their 2016 list.
Mattheus finished the Comrades Marathon twelve times, 1987- 21st, 1988 – 7th, 1989 – 9th, 1990 – 32nd, 1991 – 6th, 1992 – 1st (but disqualified), 1994 – 11th, 1995 – 2nd, 1996 – 4th, 1997 – 1st (Comrades Marathon Champion),[5] 1998 – 2nd, & 2000 – 154th.[6] Mattheus is the only athlete to lose his Comrades Marathon Champion title and regain the title a few years later, improving on his 5:42:34, 1992 [7] time with a 5:28:37 time. Dr. Charl Mattheus is now a dual United States and South African Citizen and living in Waimānalo, Hawaii, United States.[8][9]