Brian Viner's Icons of the 20th Century; No 6: Albert Einstein

Sometime in the early Fifties, it is said, Marilyn Monroe, who had a thing for brainy men, asked to meet the brainiest of them all, Albert Einstein. The Nobel prize-winning physicist was well into his seventies by then, but he was just as impressed by a substantial cleavage as Monroe was by a substantial intellect. Apparently they got on rather well, and the comedian Arnold Brown has worked their improbable encounter into a sweetly whimsical tale, which has Einstein and Monroe returning to her hotel room after dinner and making themselves comfortable on the sofa. "Albert," says Marilyn. "Vot is it, my dear?" "I hope you don't mind me asking, but would you try to explain to me your theory of relativity?" Einstein pats Monroe's leg. "I'm terribly sorry, my dear," he says, "but I neffer go zat far on a first date."

Einstein was born 120 years ago, in Ulm, Bavaria. He went to university in Zurich, took Swiss citizenship and then got a job as an examiner at the patent office in Berne. He had been fascinated by maths and physics since early childhood and quietly continued his research into various scientific phenomena without letting his colleagues know the depth of his passion. Consider, therefore, how astonished they must have been when, in 1906, Einstein became a scientist of international renown practically overnight. One day he was processing patents in Berne, the next his paper on relativity was earning plaudits from academics all over the world.

In 1916, by now a professor at the Royal Prussian Academy in Berlin, Einstein published further material on relativity, revolving around the famous equation e=mc2. This concerned the relationship between energy, mass and velocity, and remains bewildering to those of us who do not know our kilojoules from our megawatts. However, it was revolutionary stuff, and in 1919 there was further excitement when a solar eclipse confirmed his theories about light rays being deflected by the sun's magnetic field. In 1921 he won the Nobel prize.

Fortuitously, Einstein was away from Berlin lecturing at the California Institute of Technology when the Nazis came to power in 1933. He remained in the US, became a professor at Princeton and took American citizenship, and by the Forties his name was synonymous with brainpower. Indeed, my mother recalls referring to a particularly swotty classmate as "an Einstein" - which is rather humbling because, by the time I was at school, a brainy person was merely "a bit of a Bamber Gascoigne". Now, they are "a right old Carol Vorderman". How standards slip.

Just before the Second World War, American scientists learnt that their counterparts in Germany were close to developing an atomic bomb. Alarmed, Einstein wrote his historic letter to President Roosevelt, insisting that America should push ahead with its own nuclear research. Roosevelt took heed. However, when this research led to the devastation at Hiroshima and Nagasaki Einstein was horrified, and deeply troubled by his own role in the affair. He duly became chairman of a committee of nuclear scientists that campaigned for a ban on nuclear weapons. Giving the atomic bomb to politicians and soldiers, he said, was like handing a razor to a three- year-old child.

In 1952, Einstein, not an observant Jew but a keen Zionist, was invited by the Israeli prime minister, David Ben-Gurion, to become president of the infant state of Israel. He was extremely flattered but said that he did not consider himself worthy of such a position. It is hard to imagine anyone worthier.