As Arnold Schwarzenegger, California’s governor, stood at the podium of the Republican National Convention in August 2004, scanning the vast assembly, everything was fantastic. His wife, Maria Shriver, was “fantastic”, but so was working with his predecessor and arch rival, Gray Davis, during the transition. Now that Arnold was in office, every Californian would have a “fantastic job”. When a judge ruled that he had violated campaign laws and would have to repay $4.5m out of his own pocket, that was “fantastic”, too.

This was Arnold’s first public test as a national figure and the most important speech of his life. He had been governor for 9½ months, elected in a controversial recall election. As far as he was concerned he had done a fantastic job. He was wildly popular and had made Californians feel good about their state again.

He became the world’s greatest bodybuilder by the most meticulous preparation; the world’s biggest movie star through attention to every last detail of his films.

His most famous character, the Terminator, was a robot but Arnold projected himself onto the world as a Terminator with a heart, a suprahuman, regrowing his ageing parts to seem eternally young. Now he was a politician and to prepare for this evening he had spent hours with his speechwriter.

“My fellow Americans, this is an amazing moment for me,” he said. “To think that a once scrawny boy from Austria could grow up to become governor of California and stand in Madison Square Garden to speak on behalf of the president of the United States: that is an immigrant’s dream. It is an American dream.”

The applause became an ovation but Arnold did not linger. He had done precisely what he wanted to do. He could never say so publicly, but he believed that there was a vacuum of leadership in his adopted country. All that held him back from actively aspiring to the highest office in the land was the ban on foreign-born citizens becoming president.

He believed that he had been chosen for a special role in the world. He admired Charlemagne and Napoleon, who could take the inert passive masses and mould them into a force to make history.

“I admired Hitler, for instance, because he came from being a little man with almost no formal education up to power,” he said. “I admire him for being such a good speaker and his way of getting to people. But I didn’t admire him for what he did with it.”

Arnold believed that America needed a great leader with all the messianic skills of Hitler but for good, not evil: “In Germany there was a lot of unity. The German soldiers were the best and with the police force and everything.”

It was a subject with which he was intimately acquainted. The Austria into which Arnold was born on July 30, 1947 was a despairing, defeated country occupied by the Americans, British and Russians. His childhood was dominated by his father Gustav, a policeman who had joined the Nazi party in 1938 and who volunteered for the Sturmabteilung (storm troopers), serving on both the eastern and western fronts.

The emotional neglect Arnold received from his father, the merciless teasing of his elder brother Meinhard and the secret shame of Gustav’s drunken binges could have crippled many youths. Arnold developed an ability to turn his head from what was negative and hurtful and always to look beyond. But he did not forget his post-war upbringing.

In 1984 he appeared at a fundraiser for the Wiesenthal Center in Los Angeles and Rabbi Marvin Hier, its director, was astounded when Arnold donated $50,000 every time he starred in a film, making him the single largest Hollywood contributor other than the top studio executives. Hier sensed there was some other purpose behind the donations. Arnold could not deal with the emotions he felt over his father, and if his contributions were in part guilt or penance they were also indications of a search for greater understanding and knowledge.

“He understood very much what the Holocaust was and he was ashamed that Austrians did not want to confront it in reality,” Hier said.