When Bill Clinton was seeking advice on whether to choose Al Gore as his vice-presidential running mate in 1992, he was told: "This is a man who will never knife you in the back."

Gore's loyalty to Clinton has been unshakeable over eight turbulent years. Even when things were at their blackest for the President over the Monica Lewinsky affair, and Gore must have been tempted to waver just a little, he continued to call Clinton "my friend", and on the day Clinton was impeached Gore stunned Americans by calling Clinton "one of our greatest Presidents".

Gore went to Vietnam to fight in a war he detested out of loyalty to his father who was facing defeat in a Senate election because of his anti-war views, unpopular in Tennessee. The son could, like most other Harvard graduates, have got a deferment but believed he could help his father by enlisting.

Gore has been a model husband and father for over 30 years. He was one of the hardest-working members of the House of Representatives and the Senate over 16 years. Even his enemies would concede that his eight years' experience as Vice-President on top of that makes him one of the best qualified candidates for the Oval Office in US history.

And yet this superbly equipped politician is struggling to come across as likeable and trustworthy to the American people who in polls are more attracted to his much less experienced and raffish Republican rival, George W. Bush. Gore works harder than most politicians at "town meetings" where he talks to local people for hours on issues. But there is something missing in the person-to-person chemistry.

Gore is what the Americans call a "policy wonk" who can't get enough briefings. He also does his own research and probably knows more than the briefers. And he doesn't wear his learning lightly. A recent interview with the New Yorker aimed at seeing Gore as "the man he really is" at times read like the meanderings of a mad professor. At dinner parties he is ready to produce wall charts.

In conversation, Gore can drop names such as Maurice Merleau-Ponty, a French existentialist philosopher; Edmund Husserl, a German phenomenonologist; Reinhold Niebuhr, a theologian, and Teilhard de Chardin, the Jesuit paeleontologist.

In his 1992 book Earth in the Balance, warning against global warming, he was scornful of the caution which "whispers persuasively in the ear of every politician, often with good reason". He goes on: "For me, the environmental crisis is the critical case in point: now every time I pause to consider whether I have gone too far out on a limb, I look at the new facts that continue to pour in from around the world and conclude I have not gone nearly far enough."

But a few months after these words were published, Bill Clinton chose Gore to be his running mate and the road to the White House took precedence over apocalyptic warnings. Just as he was breaking out of a defensive shell, Gore was forced back into it.

Gore's father, Albert senior, would not have been surprised at his son ending up a heartbeat away from the presidency. He had had his own ambitions for the White House thwarted and later steered his son that way. "We reared him for it," his father boasted.

That rearing was unlike that of most other boys of Gore's generation. He was born in Washington where his father spent most of the year as a senator representing Tennessee. The family lived in an apartment on the top floor of a hotel on Embassy Row, and politics was part of the young Gore's daily life. But during school holidays he was sent to the family farm at Carthage, 50 miles east of Nashville, where his father insisted he do such back-breaking work that his mother protested.

In Washington, Gore was sent to St Albans National Cathedral School where sons of wealthy families studied to enter Ivy League universities such as Harvard.

Gore did well at studies but was seen as a bit of a prig who ratted on members of the football team - which he captained - for drinking instead of training. He duly made Harvard and arrived there in 1965 as the Vietnam War was escalating. Like George Bush in Yale around the same time, Gore steered clear of the big anti-war protest movement. One of his room-mates was Tommy Lee Jones, who later became a film actor.

Like most students of the time, Gore smoked cannabis. He also tried to write a Faulknerian novel set in the South.

In studies he veered from English literature towards government and politics. He followed a course on the "problems of post-industrial society" which required reading Freud and Marx. His professor, Marty Peretz, who later became a wealthy property developer and owns the political weekly New Republic, became a close friend of Gore and advises him on Middle East affairs. It was he who told Clinton that Gore was no back-stabber.

Gore had met Tipper Aitcheson, a high-spirited blonde student, while at St Albans and the relationship developed when she enrolled in Boston University to be near him. Gore got into trouble when he told journalists years later that he and Tipper were the inspiration for Erich Segal's Love Story. Segal did not even know Tipper but knew Gore slightly at Harvard.

This was to be one of a series of exaggerated claims which have dogged Gore in the past year as journalists have delved into his past. Others are that he "invented the Internet" and was the first to expose a polluted site called the Love Canal near Niagara Falls. In Vietnam, he was assigned to information and carried a rifle but never came under enemy fire, as he claimed in interviews. He came home to the US disturbed after Vietnam where he had found soldiers "stoned continuously. . . a measure of how spiritually debilitating this experience is for a lot of people." He wrote to a friend that he would go to divinity school "to atone for his sins". But he also wanted to pursue a journalistic career and worked on the Tennessean newspaper in Nashville at nights. He told friends he had no interest in politics, still deeply disillusioned at his father's defeat in 1970. Yet when a Congressional seat which had once been held by his father became vacant in 1976, Gore decided to run for it. He told his father to stay out of his campaign and won the seat, thus heading back to the Washington he had left when he went to Harvard.

AS A Congressman, Gore took more conservative positions on gun control and abortion than he was to show in later years. This has led to his being accused of opportunism by opponents, who cite his strong anti-abortion stance in the 1980s compared with his present pro-choice position.

In 1984, Gore won the Senate seat his father had lost but personal tragedy intervened during the campaign when his beloved older sister, Nancy, who was a heavy smoker, died from lung cancer. Later he adopted a strong anti-tobacco stance, citing his sister's death, but critics point out that Gore continued for years to grow tobacco on the family farm and receive funding from cigarette companies.

After two years in the Senate where he deepened his expertise on nuclear weapons and environmental issues, Gore, at only 39, decided to run for the presidency in 1988. His campaign to win the Democratic nomination was a humiliating experience and Gore showed a nasty side in attacks on Democratic rivals. But he had clearly signalled his ambition for the top post.

Yet in 1992 when he might have had a better chance, he decided against running and concentrated on writing his book, Earth in the Balance. He was also influenced by a traumatic family experience when his six-year-old son, Albert III, was struck by a car when leaving a baseball game with his father and was badly injured, losing most of his spleen.

The accident plunged Gore into a period of self-examination about where his life was heading, and some of this found an outlet in his book. His personal faith seems also to have been strengthened. He says now: "I think the purpose of life is to glorify God. I turn to my faith as the bedrock of my approach to any important question in my life." For Tipper Gore, the accident and the increasing strain of raising a young family while a politician husband was often absent, brought on a clinical depression. She recovered and now campaigns on behalf of victims of mental illness.

So Al Gore turned his back on a presidential run in 1992 and concentrated on promoting his best-seller book. But then Bill Clinton, who read the book and was impressed, came calling with an offer to join his presidential election ticket.

For the next eight years, Gore filled the second-highest post in the land and has been entrusted with more responsibilities than any other vice-president in history, such as "reinventing government" by cutting back on a bloated federal workforce and on waste. He has also negotiated international environment agreements and headed the US-Russia joint commission.

Yet for most Americans Gore appears a remote and aloof figure in the shadow of Clinton, although friends say that in private he has a wicked sense of humour and is a great mimic. Once at a briefing for Clinton before a press conference, he was told that a question could be asked about Lorena Bobbitt, charged with cutting off her husband's penis. Gore advised Clinton: "No matter what you do, be sure to use the word penis as much as possible."

This is a funny side of Gore that the public never see. This week, as he emerges from Clinton's shadow, the advisers want him to show voters the real Al Gore - a loving father and a witty man as well as a statesman in whose hands America can feel secure.