By Brian Wheeler
BBC News political reporter
The Blair/Brown partnership has always been under scrutiny
When Gordon Brown delivers his 10th annual Budget on Wednesday, many will be speculating that this could be his last.
The 55-year-old chancellor's succession to the Labour leadership is now widely assumed to be beyond doubt, with Tony Blair pledging to stand down before the next election.
While a precise timetable for his move from Number 11 to Number 10 Downing Street still eludes him, Mr Brown can at least console himself with the thought that he is the longest serving chancellor of modern times.
He reached that milestone in June 2004, when he overtook David Lloyd George, who served for seven years and 43 days between 1908 and 1915.
Mr Brown himself once said there are two types of chancellor: "Those who fail and those who get out in time."
The only question that remains is whether there will be an "orderly handover" in the next two years, or whether Mr Blair will carry on for longer, possibly triggering a Brown coup.
Many within the Labour Party believe a "coronation" of Mr Brown will be undemocratic and bad for the party.
But in the meantime - and despite the shine starting to come off his reputation for prudent financial management - Mr Brown dominates the domestic political landscape like few British politicians before him.
Gordon Brown was born in Glasgow on 20 February 1951, the son of a Church of Scotland Minister in the small Fife town of Kirkcaldy.
At 12, he was canvassing for Labour and by his 20s he was a leading political activist in Scotland.
He achieved a first class degree in history from Edinburgh University, where he went on to complete a PhD.
His early career was spent lecturing, working in television and making a name for himself in the Scottish Labour Party.
His first attempt to enter Westminster, for Edinburgh South in 1979, was thwarted by former shadow foreign secretary Michael Ancram.
But in 1983, he took Dunfermline East, a new constituency including Rosyth naval base, pit villages and coastal towns.
Entering Westminster, he came to share an office with the newly elected MP for Sedgefield, Tony Blair.
The chancellor still seems determined to play the waiting game
Within four years, Mr Brown had gained his first frontbench post as shadow chief secretary to the Treasury.
He became shadow chancellor under John Smith's leadership in 1992.
After the death of leader John Smith in 1994 he stood aside, agreeing to give Tony Blair a clear run at the leadership during a now infamous meal at the Granita restaurant in Islington.
'I just love being a dad,' says Mr Brown
The other part of the deal, that Mr Blair will one day stand down in favour of the chancellor, is the stuff of Westminster legend.
Mr Blair's supporters say such a deal never existed and endless newspaper columns - and even a television film - have been devoted to the alleged deal.
But if his leadership ambitions were at least temporarily thwarted in 1994, Mr Brown continued his devotion to politics.
During the 1997 election campaign, he is said to have worked an average of 18 hours a day, six days a week after running on a treadmill for an hour each morning.
This dedication to his career was underlined by a comment by Mr Brown's former girlfriend of five years, Princess Marguerite of Romania, the eldest daughter of ex-King Michael of Romania, who said a relationship with him was "politics, politics, politics".
Mr Brown's relationship with his younger Downing Street neighbour remains the focus of intense scrutiny
If that was true then, Mr Brown, who married PR executive Sarah Macaulay in 2000, changed his perspective when the couple were hit by tragedy early in 2002.
Their daughter Jennifer died in Edinburgh Royal Infirmary, 10 days after being born seven weeks prematurely.
A year later, in October 2003, the couple had a son - John - an event which again showed a softer side to the chancellor.
In January, 2006, they announced that they were expecting a second child in July, with a happy Mr Brown telling GMTV: "I just love being a dad... it's just the best thing in the world."
Infact, 2006 has been the year in which the formerly serious and somewhat staid chancellor has undergone something of a makeover.
He smiles a lot more, revealing startling white, allegedly "enhanced" teeth, is more jovial at question time and has ventured into making policy pronouncements in any area of government he fancies.
He recently announced that law-abiding youngsters would be given vouchers worth up to £25 to spend on sports and leisure facilities.
And he showed off his "hard man" credentials in February, with a speech calling for tougher security measures to tackle the threat of global terrorism, plus a staunch defence for the new offence of the glorification of terrorism.
Despite constant stories about feuds between the Treasury and Number 10 - and the best efforts of the opposition to portray Mr Brown as a "roadblock" to reform - the ideological differences between the chancellor and Mr Blair remain relatively modest.
The most recent high profile sign of differences came from Mr Brown's devotion to means-testing in pensions, and the tax credit system he devised in 1997, which has seen him at odds with Mr Blair in the field of pensions and welfare reform.
The chancellor was furious at being portrayed as the man who tried to torpedo the Turner Commission's report into the pensions crisis, which recommended a rise in the basic state pension and a later retirement age and less reliance on means testing.
Number 10 had been equally hostile to the element of compulsion favoured by Turner, Mr Brown's allies point out.
The chancellor ordered an inquiry into the leaking of a letter detailing his concerns ahead of the Turner report, with some of his allies suggesting it had come from the Blair camp.
Yet Mr Brown has been at pains in recent speeches to stress he would, like Mr Blair, govern from the centre ground - as he faces the prospect of battling for the centre ground with the Conservative leader David Cameron.
It seems that the lurch to the left dreamed of by some in the parliamentary party looks likely to remain just that.