In 1948, UK neurologist Sir Ludwig Guttman, who worked with war veterans suffering from spinal injuries, added sport into his patients' rehabilitation program.

Others started copying Guttman's methods, and athletic competitions ensued. At the 1960 Olympics in Rome, Guttman brought 400 wheelchair athletes to compete in the Parallel Olympics. Since then, the Paralympics have gone from strength to strength.

Muhammad Ali, first called Cassius Clay, won Olympic gold in Rome in 1960.

Back in the US, when Clay was refused service in a whites-only restaurant, he threw his Olympic medal into a river. Thirty-six years later, Muhammad Ali lit the flame at the 1996 Atlanta Games, and the International Olympic Committee presented him with a replacement medal.

At the Mexico Games in 1968, African-American athletes Tommie Smith and John Carlos won gold and bronze in the 200m sprint respectively.

During their medal ceremony, they raised their fists in a "Black Power" salute while the flag was being raised and the national anthem played. Their demonstration took place amid the US civil rights movement, and the non-violent gesture of the two athletes brought international recognition to the struggle for civil rights.

During the 1972 Games in Munich, a Palestinian terrorist group Black September took hostage and killed 11 members of the Israeli Olympic team, shattering the image of international cooperation and friendship associated with the Olympics.

25 Countries staged a boycott of the 1976 Olympic Games in Montreal. They were outraged that New Zealand, whose rugby team had toured South Africa in the year despite the country being under apartheid, was allowed to take part in the 1976 Olympics.

The foreign minister of Kenya at the time, said in a statement: “The government and the people of Kenya hold the view that principles are more precious than medals.”

Australian athlete Cathy Freeman, one of 11 Aboriginals in the host nation's team, was under pressure to perform in the Sydney Games in 2000. It was hoped her performance could help promote the image of a modern, tolerant Australia.

Freeman was chosen to light the Olympic flame, but her real focus was the 400m, which she won comfortably, becoming Australia's 100th Olympic champion in the process.

The North Korean and South Korean teams marched as one at the opening ceremony of the 2000 Games in Sydney.

Female basketball player Chung Un Soon from South Korea, and Park Chong Chul, a male judo coach from the North, led the united teams. The teams were holding hands and wearing identical uniforms.