Ian Thorpe has overtaken Murray Rose as Australia's most successful male Olympian, winning his fourth Olympic gold medal.

Thorpe joined Rose as the only men in Olympic history to have won back-to-back 400m freestyle titles.

As he has done for the past seven years, Thorpe beat teammate Grant Hackett for the gold medal.

American Klete Keller won bronze.

The victory gives Thorpe four Olympic gold and two silvers while Rose won four gold, one silver and a bronze from his two Olympic appearances in 1956 and 1960.

The 21-year-old clocked 3 minutes 43.10 seconds to beat Hackett by just 0.26s.

Thorpe almost didn't swim the race after being disqualified at the Olympic trials in March for a false start.

But his friend of seven years, Craig Stevens, gave up his Olympic berth to allow the world recordholder to defend his title.

Stevens held an Australian flag aloft in the stands at the Olympic aquatic centre after Thorpe's victory.

Thorpe's time was more than three seconds slower than his world record of 3:40.08 set at the Manchester Commonwealth Games two years ago.

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