Although the 47-year-old champion kayaker retired after finishing the K1 competition without a medal, her incredible achievement rounded off a long and spectacular career that has seen her compete for both West Germany and Italy.
Idem, who saw off competition from rivals less than half her age, made it to the final at Eton Dorney. Her success is testament to the fact that she still trains for four gruelling hours every day, despite having two children and after racking up four decades of competitive sport.
Since taking up sprint canoeing in 1977, she has amassed five Olympic medals, including a gold at the 2000 Games in Sydney, and a total of 35 international titles.
Born in West Germany, she became an Italian citizen by marriage in 1990 and is the first woman from her adopted country to win both world championship and Olympic titles in canoe sprint.
Idem began paddling at the age of 11, and two years later, in 1977, she took gold over 200m, 500m and 1,000m at the European Championships in Plovdiv, Bulgaria, as well as bronze in doubles kayaking. It was the beginning of a glittering career on the water.
At Los Angeles in 1984, she won a bronze medal in the K-2 500m with Barbara Schüttpelz before switching to individual events. Four years later in Seoul, she could muster only ninth place in the K-1 500m and fifth in the fours.
But a new coach, Gugliemo Guerrini, whom she later married, brought success. Their partnership immediately reaped rewards, with Idem winning two bronze medals at the World Championships in 1989.
She competed under the Italian flag at the 1992 Barcelona Games, placing fourth – then won bronze in the 500m event at the 1996 Olympic Games in Atlanta.
Over the course of the next six years, she won three world championship titles, along with 10 silver and bronze medals, five European titles. Then came the breakthrough, when she took gold in Sydney.
After taking time out to have a child, she returned to the sport at Athens in 2004 and won a silver medal in the K-1 500m event.
At Beijing in 2008, her seventh Olympic appearance, she won a fifth medal, the silver in K-1 500m, after being pipped at the post and losing in a photo-finish.
After making it to the K1 final in London, Idem gave a hint of the dedication that goes into becoming an Olympic champion. She said: “Every day you have to work on your motivation. You always have to think about it. You go out really tired, you go out with bad weather, you go out with problems at home. But you have to go. This is it – the effort you have to put in if you want to succeed. I am very lucky. Many people do the same amount of work as I do and they don't go to the Olympics so my motivation comes from the fact that I was lucky and I was good all these years.”
Her Olympic career is now over, but Idem has promised to be at Rio in 2016 – as a journalist covering the Games.