When Gerhard Schroder got married for the fourth time earlier this year, the guests included tycoons and television stars, but his most senior colleagues in Germany's Social Democratic party were nowhere to be seen. Those who know Schroder, who hopes to deprive Chancellor Helmut Kohl of a record fifth term in office at next Sunday's federal election, were not surprised by his choice of guests.

After all, like Tony Blair and Bill Clinton before him, he is wooing voters on a non-ideological programme and putting as much distance as possible between himself and his party.

Schroder relishes the frequent comparisons made between himself and Blair as modernisers who have made the centre-left electable after long periods of conservative government.

But he has more in common with Clinton, not only on account of his weakness for women and fondness for fine cigars but because he is driven by a relentless ambition rooted in an impoverished childhood. Schroder has twisted and turned on policy issues so many times that even his closest associates are unsure of what he really stands for.

But what nobody doubts is that he represents the best chance for a Social Democratled government since Kohl came to power 16 years ago.

Not long after he entered the Bundestag in 1980, Schroder was coming home after a night of drinking in Bonn when he passed the chancellery. Rattling the gates violently, he roared: "I want to get in there."

But he admitted in his memoirs that he felt a lust for power much earlier, when he was a 14-year-old sales assistant in a general store in the northern town of Lemgo.

"Power fascinated me from the moment that I stood behind a counter as an apprentice, with no educational qualifications and no prospects. I wanted to get out of there, to make something happen," he wrote.

Gerhard Schroder was born on April 7th, 1944, just three days before his father died fighting for "Fuhrer, Volk and Vaterland" in Romania. His mother Erika, who is now 84, rose at five each morning to work as a cleaner, leaving the young Gerhard to take care of his sisters and to deal with the bailiffs who regularly called to the door.

"We lived for a long time on social security. That shapes you. It also makes you sensitive. Whenever this issue comes on the agenda, I immediately remember these times," he said.

In the evenings after work in the shop, Schroder went to school and completed his Abitur, the equivalent of A Levels, in 1966 - at the age of 22. He decided to study law and, while still a student, married his childhood sweetheart, Eva Schubach.

The marriage lasted just three years, not least because Schroder's growing interest in politics was occupying most of his time. In 1972 he married a student activist, Anne Taschenmacher, whom he had met at a meeting of the Young Social Democrats, or Jusos.

By the time Schroder became leader of the Jusos in 1978, he had a reputation as a left-winger who had defended ex-terrorists and opposed the stationing of US nuclear missiles in Germany. But he made his peace with the Social Democratic party leadership in time to win a nomination for a Bundestag seat in 1980.

During this campaign, he met Hiltrud Marion Hampel, a 31-year-old political scientist who became his third wife and with whom he formed a political partnership unique in Germany.

As the Social Democrats lost one federal election after another, Schroder focused on becoming prime minister of his home state, Lower Saxony. When he succeeded in 1990, it was at the head of a coalition with the environmentalist Greens, an arrangement that was almost untested at the time.

Schroder had shed many of his left-wing views by the time he came into office, but power itself changed him, too, as the conservative Frankfurter Allgemeine newspaper noted.

"Before the eyes of the public, Schroder has undergone an astonishing personality change. The wounded aggressiveness of the opposition leader has become relaxed joviality, the stilted wish to impress has been replaced by the cool, governing style of an unassailable officeholder," it wrote.

Hiltrud, known as Hillu, was among his most valuable political assets, providing a caring, environmentally aware counterbalance to his own robust, pragmatic image.

They were Germany's first political couple to court the media and to present themselves as stars, moving in ever more exalted company. Schroder began to spend less time with party activists and trade union officials and more with business leaders such as Volkswagen chairman Ferdinand Piech.

He espoused new, business-friendly politics and abandoned much that remained of his left-wing ideology, including his opposition to changes in Germany's policy towards asylum-seekers. Even Hiltrud was shocked: "I was annoyed by the brazen way he presented his U-turn. He met two ladies at tennis who complained that their gym hall was full of refugees and they couldn't shower. `Then I knew we had a problem,' Gerhard said."

Schroder's flirtation with the rich reached its climax in February 1996 when he and Hiltrud attended the Opera Ball in Vienna, along with Piech and his wife. A local paper published a photograph of them, the men in white tie and tails and the women in expensive formal dresses, sitting in Piech's DM28,000 (£11,200) box.

The ball not only banished any doubts about where Schroder's political heart lay; it was also the last waltz for himself and Hillu. A few weeks earlier, Schroder had met a 31-year-old journalist called Doris Kopf and the couple were photographed flirting during a visit to Norway.

When Schroder discovered that the press knew about the story, he drove home to his wife and told her what had happened. It was approaching midnight but Hiltrud insisted that he leave the house immediately.

"He didn't want to take a taxi into Hanover with all his things so I drove him there. It was the last service I did him," Hiltrud recalls.

The fourth Mrs Schroder declines to make any political comments in public but she has been advising the candidate on how to dress and, through her friends in the media, helping him to maintain his already friendly relations with the press.

Schroder has foresworn alcohol and his beloved Havana cigars until the results come in next Sunday. Opinion polls continue to predict that he will become the first Social Democrat to govern Germany since Helmut Schmidt. If he loses, he will continue as prime minister of Lower Saxony and, if past form is anything to go by, contemplate his next bid for power in four years' time.