They have been called the Lennon and McCartney of politics: visionary harbingers of generational change, international A-listers with a global following, formidable partners so intertwined it is hard to think of one without the other.
But British Prime Minister Tony Blair and Chancellor of the Exchequer Gordon Brown may wince at the analogy. After all, John and Paul's harmonies eventually gave way to discord and dissolution. And Britain's foremost political relationship has long since fallen flat.
Every few months a new set of anecdotes swirls around Westminster, detailing the strident antipathy that supposedly divides the prime minister and his right-hand man.
Yet for all the attention given to conflicts between Brown and Blair, their relationship is perhaps most remarkable for what it has not done: create gridlock. Indeed, the rivals have presided over what has been, by most measures, a fairly ambitious and quite functional government.
The situation puzzles political observers. After all, dissident acolytes are little tolerated in other polities. It's hard to imagine Presidents Bush or Vladimir Putin sitting back while a rival schemes for their job.
With Britain heading for a likely May general election that Labour is expected to win again, the longstanding rivalry raises several questions. Why has it festered so long? And why has Blair not dispensed with his turbulent chancellor?
"Life is very short," sang John and Paul, "and there's no time for fussing and fighting my friend." Political life is even shorter, but so far Blair and Brown have not let rancor end their careers.
The press have dubbed the bickering the "TB-GBs." Some say it dates to 1994, when Blair leapfrogged Brown to lead the Labour Party, making his old friend a mere sidekick.
The strange quality to this rivalry is that both men know they need each other.
Brown has an impressive eight-year economic track record that has undermined the claim that Labour cannot manage the economy. Subdued inflation, high employment, low home-loan rates, successful antipoverty measures - it's a list that Blair himself praises.
The chancellor of the exchequer is also more popular with traditional Labour, a constituency Blair cannot afford to alienate, particularly as many are still unhappy about the Iraq war.
"That is the difference between the prime ministerial and presidential systems," says John Curtice, professor of politics at Strathclyde University in Glasgow, Scotland. "Mr. Brown has his own power base within the party and cannot be ignored."
But Brown likewise cannot do without Blair. The telegenic prime minister is still more likely to appeal to wavering, middle-class voters than his aloof, intellectual counterpart. One commentator has likened it to the fable of the frog and scorpion, both needing each other to cross the river. Ominously, in that tale, the scorpion stings the frog and they both drown.
"Brown is in a suicide-bomber situation," says David Baker, professor of politics at Warwick University near Coventry, England. "He can take out the prime minister, but he will have to detonate himself to do it. And Labour will be out of office."
The ideological gap between the two is quite small. Sure, a few differences have affected policy. Brown was notably skeptical about adopting the euro, an issue that has, for now, been shelved. He also queried free-market tinkering with hospitals and higher education.
But the two have a similar vision for Britain. They make the same appeals for equality, opportunity, and social justice. Both advocate poverty relief for developing nations. And if Brown had misgivings about Blair's support for war in Iraq he never breathed a word about it.
In short the differences appear to be more about style than substance. Brown may see himself as more radical - he even occasionally uses the dreaded "S" word, socialism - but his economic stewardship has been utterly Blair-like: pragmatic and moderate.
Strange though their relationship is, it is not unique. Britain has a long culture of rivalry in politics. Most prime ministers since World War II have had to deal with ambitious, frustrated colleagues.
The 1960s rivalry between prime minister Harold Wilson and his right-hand man George Brown share some features of the Blair-Brown feud: a pragmatic prime minister and a tempestuous deputy who feels frustrated by having been overlooked for the top job.
A similar rivalry emerged in the 1980s between Margaret Thatcher and her chancellor Nigel Lawson. In both these cases, the prime ministers waited for their rival to fall on his sword.
Blair did the same when challenged over Iraq by senior cabinet members. He waited for them to resign rather than sacking them.
"In Britain, there is a tradition for allowing this kind of criticism," says Professor Baker. "There is an understanding of the frustration that builds up because of the sheer unalloyed power of the British prime minister. If he doesn't let the dogs off the leash occasionally, they'll bring the house down."
Nigel Nicholson, professor of organizational behavior at London Business School, says wherever there is hierarchy, there will be rivalry.
But he adds that clever leadership can harness rivalry into being a positive force by encouraging creativity, allowing talent to flourish, and above all by ensuring an open and fair succession procedure.
"The way leaders handle succession issues is very critical," he says. "Some treat it as if they were their sons slugging it out for dad's crown and it gets a bit Shakespearean."