Fondly known as Oom Wietse, Van der Westhuizen, 59, is one of five runners who will be honoured with a "quadruple green" number at the ultra marathon next week.
A runner receives a green number once they’ve completed 10 Comrades, with more garlands added every subsequent 10.
“I do not take any of this for granted, I feel really blessed,” Van der Westhuizen said. “I still cry at the start of Comrades. It’s a special race. It is different to any of the races I have done.”
Growing up in Johannesburg, Bellville resident Van der Westhuizen started running at school. He did cross-country and competitive walking before a friend introduced him to the Two Oceans Marathon.
“When I finished, I received a pamphlet about the Comrades Marathon and I decided to do it. I never looked back,” he said.
His daughters Louise and Wilandi also run, while his wife Wilna is their biggest supporter.
Asked about running his 40th Comrades, Van der Westhuizen said: “When I was younger, I chased targets and I would race hard, but now I am going just to finish the race.”
Van der Westhuizen runs five days a week, and has his own popular training programme.
“I hate running alone. People think I did the programme for them. No, I am just using them to run with me,” he said. “My dream is to take a couch-potato guy from a 5km park run, to run the Comrades."