Gordon Brown, the treasury chief who guided Britain through sweeping economic reforms, is the most formidable figure in Prime Minister Tony Blair's Cabinet and his heir apparent.

Brown stripped the government of its power to decide interest rates and put them in the hands of the independent Bank of England (search). And he has been a decisive figure in ruling out Britain's entry into the European Union single currency system any time soon.

The rivalry between Brown and Blair has been intense, and Brown is said to covet the premier's post. Brown became a vital crutch for Blair during the campaign, after the prime minister's credibility slumped because of the Iraq war.

Blair won re-election with his Labour Party (search) gaining a majority in the House of Commons (search) in Thursday's voting, official results showed. But the party suffered a sharply reduced parliamentary majority — less than half its current 161-seat margin.

The results could set the stage for Blair to be replaced in midterm by Brown, widely credited for the strong economy that appears to have clinched Labour's victory.

Also in Thursday's vote, Brown won a newly drawn House of Commons seat in Scotland. Brown said that he was humbled to be declared a member of the new Parliament representing the area of Scotland where he grew up.

"If, as I believe will happen, a Labour government will be elected for a historic third term, our purpose will be to maintain and entrench our economic stability and prosperity, ... and to build a stronger, fairer Britain," he said.

Ideologically, there is little difference between the two men. Both oversaw a transformation of the Labour Party in the 1990s, dumping much of its socialist ethos in a bid to court big business and middle class voters.

Like Blair, Brown supports reforming public services and introducing greater private sector involvement in state-run health care and education. But Brown is seen as more in touch with Labour's socialists roots and is more popular with leftist sections of the party that have grown disillusioned with Blair.

"Brown knows the Labour Party much better, he is more a creature of the party," said Geoff Andrews, political analyst at the Open University.

After stints as a politics lecturer and television editor, Brown was elected to the House of Commons in 1983, the same year as Blair, and quickly made his mark on the party with his hard work and sharp intellect.

When Labour leader John Smith died in 1994, Brown was a favorite to succeed him. But he grudgingly took the advice of party insiders and stood aside in favor of Blair.

Blair and Brown were widely reported to have reached an understanding — never formally confirmed — that if Labour won power, Blair would step down after about six years and let Brown take the helm. That date passed some two years ago, and tension between the men is palpable.

The son of a Church of Scotland (search) minister, Brown is married and has one child. His Scottish-accented oratory can be plodding even when fiery, and he seems to wear a permanent scowl of concern.

As Chancellor of the Exchequer (search), Brown has overseen eight years of low inflation, low unemployment and low interest rates, and, according to Blair, is Britain's best Treasury chief in 100 years.