For a decade, the brooding figure of Gordon Brown has held sway over the British political landscape in a way that no other modern politician outside the office of Prime Minister has achieved.

From his powerbase at the Treasury he has wielded greater influence across the full range of domestic policy than any previous Chancellor of the Exchequer.

An intense, complex, sometimes awkward, driven man, he has inspired both admiration and enmity among political colleagues and opponents alike.

Few at Westminster can match his intellectual grasp and mastery of detail, but his reliance on a close-knit group of aides and his open disdain for views other than his own, have earned him numerous enemies.

One senior Whitehall mandarin who observed him at close quarters for many years said recently that he demonstrated a "Stalinist ruthlessness" in his dealings with colleagues and rivals.

He has been yoked in uncomfortable partnership with Tony Blair since their famous pact struck in the Granita restaurant in the fashionable Islington district of north London, following the death of then Labour leader John Smith in 1994.

While Mr Blair has at times been driven to exasperation by his troublesome Downing Street neighbour, he knows also that he has been utterly indispensable to the New Labour project.

Now, as he prepares to claim the political inheritance which he has long believed is rightfully his, Mr Brown will have to convince colleagues and country that he is not the "control freak" of myth and can truly lead as well as dominate.

Born on February 20, 1951, James Gordon Brown's political credo was forged at the feet of his father, John, a minister in the Church of Scotland.

From him, he absorbed a burning belief in the need for social justice combined with an almost puritanical sense of rectitude and certainty in his own beliefs.

Academically gifted, the young Gordon Brown was fast-streamed through the school system, entering Edinburgh University at the age of just 16.

There, five years later, he upset the establishment by becoming elected rector - a post normally reserved for a distinguished public figure.

His fierce ambition to succeed was given a further spur by a schoolboy rugby accident which left him blind in one eye, with the knowledge that he could lose the sight in the other at any time.

After university, there were spells as a lecturer and a television journalist before entering Parliament in 1983 as part of the same intake of new Labour MPs as Tony Blair - the man with whom his career was to become inextricably entwined.

The two talented newcomers even shared a Commons room. Initially, it was Mr Brown who made the bigger impact with a series of high profile social security leaks.

Within two years he had won a place on the Labour front bench as a trade and industry spokesman and in 1987 he entered the shadow cabinet for the first time as shadow chief secretary to the Treasury.

He quickly gained a reputation as a formidable Commons performer and after Labour's 1992 general election defeat he was promoted by new leader John Smith to the post of shadow chancellor.

Mr Brown was by now established as the clear leader of the younger generation of Labour "modernisers", determined to make the party electable again, after more than a decade in the political wilderness.

It came as a shock when, in 1994, following the sudden death of Mr Smith, the talk at Westminster was of Mr Blair as the modernisers' choice to become new leader.

Crucially, Peter Mandelson, the party's communications chief and arch manipulator, concluded that it was the media-friendly family man, Mr Blair, who could best reach out to Middle England, rather than the dour, introverted Scot, Mr Brown.

Over a tense dinner at the Granita restaurant, Mr Brown agreed to stand aside for his younger colleague in return for a promise of far-reaching control over domestic policy once Labour were in government.

What is not known - but has been endlessly speculated upon - is what Mr Blair said about when he would step down and hand over the top job to Mr Brown.

What is certain is that Mr Brown came away with a bitter sense of resentment, which has run like a faultline through Labour politics.

As shadow chancellor, however, his immediate task was to convince voters that Labour had abandoned its "tax and spend" ways of the past and could now be trusted with the economy.

His advocacy of "post neo-classical endogenous growth theory" may have been mocked, but his promise to stick to tight Tory spending plans for the first two years of a Labour government was not.

After Labour swept to power in the general election landslide of May 1997, Mr Brown began his tenure at the Treasury with an audacious masterstroke - springing the surprise announcement that interest rates would in future be set by the Bank of England.

But while Mr Brown was revelling in his reputation as the "iron Chancellor", the tensions bubbling underneath soon surfaced, with the first of the numerous bouts of semi-public feuding with Mr Blair.

Amid briefing and counter-briefing by allies of the two men, one No 10 aide woundingly described the Chancellor as "psychologically flawed" - a jibe he never forgot.

It was to set the pattern for years to come, with outbreaks of feuding punctuated by periods of more-or-less calm.
There were clashes over public service reforms and over Mr Blair's ambition to take Britain into the euro, which Mr Brown effectively frustrated with his famous five economic tests.

No 10 aides would complain that Mr Brown was so secretive he would not tell Mr Blair what was in his budgets until the last minute.

Mr Brown was in turn furious when, after the 2001 election, he agreed to loosen the purse strings, Mr Blair effectively pre-empted his announcement of a massive cash injection for the National Health Service.

Mr Brown's tendency to interfere in the work of other departments through Treasury-set performance targets became a source of resentment among other, less powerful colleagues.

Critics complained that his budgets - invariably culminating with a stroke of political theatre on the day - would subsequently unravel under detailed scrutiny of the figures.

In the Commons, opponents were mercilessly steamrollered - bludgeoned into submission with great barrages of statistics rattled out at breakneck speed. It may not always have been pretty, but it was certainly effective.

However, with the economy enjoying a prolonged period of steady growth, combined with low inflation and low interest rates - in marked contrast to the turbulence of the early 1990s - Mr Brown could largely afford to ignore his critics.

He remained hugely popular among grassroots activists - many of whom never fully trusted Mr Blair. To the party traditionalists, it was Mr Brown - Labour through and through - who was the "keeper of the flame" among the New Labour high command.

Unlike Mr Blair, Mr Brown was not afraid to engage in the odd bout of old-fashioned class warfare - most famously when he accused Oxford University of elitism over its failure to offer a place to state school pupil Laura Spence, even though she achieved top A-level grades.

Public prominence inevitably brought with it greater interest in his private life - and questions as to why - in his late 40s - he remained unmarried. To his obvious discomfort, he was even asked by Sue Lawley on Desert Island Discs whether he was gay.

That changed in 2000 when he finally married his long-term girlfriend, PR executive Sarah Macaulay, confounding sceptics at Westminster who believed their romance was going nowhere.

Mr Brown could scarcely contain his delight the following year when his wife gave birth to a daughter, Jennifer Jane - only to see his joy turn to despair when she died 11 days later.

The couple went on to have two sons. Last year it was disclosed that the younger boy, James Fraser, had been diagnosed as suffering from cystic fibrosis.

Allies of the Chancellor believe that the experience of family life has softened his at-times brusque public image, enabling him to present a more human side to his character.

With Mr Blair on his way out and the great prize of the premiership almost within his grasp, the question now for this most complex of politicians is how much - and for how long - will he enjoy his political inheritance.