As a 17-year-old, Aaron Peirsol finished .59 seconds behind swimming great Lenny Krayzelburg in Sydney. Since then, he has rarely finished second.

The 21-year-old American won his second gold medal at the Athens Olympics on Thursday after winning an appeal against his disqualification from the men's 200 metre backstroke. He had already won the 100 metre backstroke.

He led from start to finish to easily win the race five meters ahead of Austrian Markus Rogan only to learn he had been disqualified for an illegal turn on the last lap.

But Peirsol was quickly reinstated after convincing officials he had done nothing wrong, allowing the U.S. to clean up three of the four gold medals on offer in the pool on Thursday.

Piersol first shot to prominence when he won his first world title in 2001, in the 200m backstroke in Fukuoka, Japan.

He continued his dominance in that event the following year, going 1:55.15 seconds at the U.S. Spring Nationals to break Krayzelburg's world record.

He also won the 100m backstroke, and repeated the backstroke double at Summer Nationals. A week later, at the Pan Pacific Championships, Peirsol swept the 100m and 200m backstrokes and helped the U.S. medley relay team to a world record.

In 2003, he added world titles in both backstrokes and drove the U.S. to a 4x100m medley relay world record.

Peirsol says one of his goals is going undefeated the rest of his career and going by his huge victory margins he just might manage to do that.

Aaron Peirsol, our Olympian of the day.