Here's just a selection.
Australian swimming star Dawn Fraser, gold medallist in three successive Games, was the youngest of eight children. Always in the water, racing her brothers, she was spotted by a coach who brought her to the point where at the 1956 Olympics in Melbourne she won the 100m freestyle, going on to repeat the feat 1960, in Rome, and again in Tokyo in 1964.
Much loved by her fellow Australians, who admire her feisty and sometimes undisciplined ways, she was given a magnificent welcome when she carried the torch at the 2000 Sydney Games.
Born in Austria, Weissmuller came to America at the age of seven months with his parents. He won five gold medals in two Olympics - 1924 and 1928 - and in his career he set 28 world records, an achievement that for many makes him the greatest swimmer of all time. After his swimming career, Weissmuller became a movie star, achieving undying fame and showing off his swimming abilities as Tarzan in 12 films. A much-admired man, he was a friendly giant. One of his friends said: "Working with Big John was one of the highlights of my life. He was a Star with a capital S." He died in 1984.
Dame Mary Peters
The expression "Putting something back" is brought triumphantly to life in the record of Mary Peters of Great Britain, whose successful athletics career has been wonderfully crowned by years of work in the service of others. She won gold in the pentathlon in the 1972 Munich Games. In 10 years of competition she set 25 British records. Her competition days behind her, she set about giving her name and her energies to a wide range of charities always with her roots in Northern Ireland. She has been honoured many times, culminating in being made a Dame of the British Empire in 2001.
As a young man Bikila saw athletes returning from the Melbourne Games wearing "Ethiopia" tracksuits, and he determined to be one of them. Sure enough, in 1960, in Rome, he won the marathon, the first African athlete to do so. The sight of Bikila running, barefoot, up the torchlit Appian way to finish under the Arch of Constantine, was one of the great Olympic moments.
Then in Tokyo in 1964 he repeated the feat, one of the few to have done so - and only six weeks after an operation for appendicitis. Bikila's later life was beset by tragedy. Paralysed by a motor accident, he took part in some wheelchair events, but died in 1973 at the age of 41.
Alfred Oerter is the greatest discus thrower ever. He won the event at four successive Olympic games - 1956, 1960, 1964 and 1968. He made a comeback in the late 1970s and threw his personal best in 1980 at the age of 43. Only injury kept him out of the trials for the 1984 Games. In 1960 Oerter was up against his rival Richard Babka. When Babka was leading, he gave Oerter some advice about his technique. Oerter thanked him, took the advice and won.
The queen of women's athletics in her time, Francisca ("Fanny") Blankers-Koen of Holland saw her prime years stolen by the Second World War, during which she suffered malnutrition during the German occupation.
But in 1948, at the age of 30, with two young children, she won four gold medals in the London Olympic Games - the 100m, 200m 80m hurdles and 4 x 100m relay. Her career continued until 1955, and in 1999 she was nominated "Female Athlete of the Century" by the International Amateur Athletic Federation.
James Cleveland ("Jesse") Owens was born into a poor US family, but his name is forever linked with the 1936 Olympics in Berlin where he won four gold medals - 100m, 200m, long jump and sprint relay in front of Hitler, at an Olympics intended to showcase German racial superiority. His family still administers the Jesse Owens Foundation, which helps young people achieve their ambitions.