Wayde van Niekerk smashed the 400m world record with a time of 43.03 seconds.
He achieved this feat at the Rio Olympics, beating American Johnson's 1999 mark of 43.18 seconds.
What happened?
Van Niekerk got off to a strong start in lane eight and was streaking clear on the back straight.
He upped his pace even further to better Johnson's record.
Van Niekerk told reporters, "I believed I could get the world record, I've dreamed of this medal since forever."
Why it matters for Wayde van Niekerk
The South African flew across the line a good five metres ahead of 2012 champion Kirani James.
James took silver in 43.76 seconds and LaShawn Merritt of the United States claimed bronze in 43.85.
This was the first time the top three had run under 44 seconds in the one-lap Olympic final.
What comes next?
Van Niekerk marked himself as the leading contender for Rio when he led home Merritt and James with an exceptional run to win gold at last year's world championships in Beijing.
He became the first sprinter to run the 100 below 10 seconds, 200 under 20 seconds and 400 in less than 44 seconds.
American Johnson was dumbfounded by the quality of Van Niekerk's finish, saying "Oh my God, from lane eight, a world record."
Van Niekerk's win was a historic moment in the sport, with many considering it one of the greatest performances of all time.
The 24-year-old world champion was overwhelmed with emotion after the race, holding his hands to his head in disbelief.
He was embraced by Kirani James, who congratulated him on his achievement.
Van Niekerk's record-breaking performance has cemented his position as one of the greatest sprinters in the world.
He will look to continue his success in future competitions, with his sights set on breaking more records and winning more medals.
Van Niekerk's success is a testament to his hard work and dedication to the sport.
He has inspired many with his achievements and will continue to be a role model for young athletes around the world.