Australia by far.
As of the 2008 Games, since the modern Olympics began in 1896, the United States has won the most gold medals (896) and total medals (2191) in the Summer Olympics. The Soviet Union/Russia is second in both gold (395) and total (1010) medals. Since the Winter Olympics began, Norway has won the most gold (98) and total (280) medals in the Winter Games. The United States and Soviet Union/Russia are tied for second most gold medals (78) and the US is second in total medals (216) and the Soviet Union/Russia is third (194).
Nigeria has won 14 gold medals in olympic since 1960.
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Micheal Phelps
As of a day or so ago they had won no medals. Iraq has only won one medal since they began participating in 1948. It was a bronze in weight lifting.
14 medals after the 2012 Olympics.
Dara Torres has won 4 gold Medals since the 1984 Olympics.
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The United States.
The United States led the London 2012 Summer Olympics, with 46 gold medals. That was the most ever by a US team in a non-boycotted Olympics since 1904.
Through the 2008 Games in Beijing: 4705 gold medals have been awarded in the Summer Olympics since 1896. Great Britain has won 207 of them. This is a percentage of 4.40. 774 gold medals have been awarded in the Winter Olympics since 1924. Great Britain has won 8 of them. This is a percentage of 1.03.