Ahead of his speech to the Labour Party Conference in the UK this afternoon, Sean O'Hagan of The Observer profiled Bono's campaigning work.

(If you are in the UK you can catch most of the daytime highlights of the Labour Conference on BBC 2 while the BBC's Parliament channel (Sky Satellite Channel 508) has the conference all day long.)

'He's as big a campaigner for the poor and hungry as he is a rock star, but what really singles him out is that when he speaks, as he will at this week's Labour Party conference, world leaders listen

Bill Clinton likes to tell a story about the first time the world's biggest rock star visited the White House. 'I'll never forget one day, during my administration, (Treasury) Secretary (Lawrence) Summers comes into my office and says, "You know, some guy came to just see me in jeans and a T-shirt, and he just had one name, but he sure is smart. Do you know anything about him?"'

These days, Lawrence Summers holds court at Harvard, and remains one of America's foremost economists. Having served his time with Clinton, he is now, ironically, an unofficial adviser to the scruffy guy in the jeans and T-shirt, who still has has only one name. He is called Bono, and there is not one person on Capitol Hill who does not now know who he is, or what he is attempting to do.

According to President George W Bush, whom, one suspects, is less enamoured of the cult of rock celebrity than his wayward predecessor, 'Bono has a willingness to lead, to achieve what his heart tells him, and that is nobody - nobody - should be living in poverty and hopelessness'. To this end, Bono is now a global figurehead for the campaign to rid Africa of Aids, and free the continent from debt. Even the extreme right of the Republican Party have been swayed by Bono's charisma and integrity. 'You can see the halo over his head,' said Senator Jesse Helms of North Carolina, a man not given to irony or overstatement.

In rock'n'roll terms, that halo once meant that Bono, and his group U2, were initially greeted by a degree of suspicion by the critical cognoscenti, who prefer their icons to be tarnished or, better still, dead. But 25 years on, Bono has broken the rules, not just of rock'n'roll, but of modern celebrity, being neither a dabbler in good causes, nor simply a famous fund raiser, but by becoming an effective and dedicated long-term campaigner, and one whose knowledge of the minutiae of the global economy and debt relief has astonished many politicians.

'I refused to meet him at first,' admitted former US Treasury Secretary Paul O'Neill, who alongside Colin Powell and, even more surprisingly, right winger Jesse Helms, is now one of Bono's many sympathetic Republican contacts. 'I thought he was just some pop star who wanted to use me.' Their scheduled half-hour session overran by an hour. 'He's a serious person,' O'Neill said. 'He cares deeply about these issues, and you know what? He knows a lot about them.'

In the past few years, Bono has met and won over two American Presidents, as well as the Pope, President Putin, multi-millionaire George Soros and UN Secretary Kofi Annan. According to Oxfam's Adrian Lovett, who helped form Jubilee 2000, the Bono-driven debt relief campaign that preceded Data (Debt Aids Trade Africa), 'the decisive moment on debt was June 1999 at the G8 Summit in Cologne where an extra £50 billion was promised. It wasn't all down to Bono, of course, but it would never have happened without him'.

Bono will make history again this week when he follows Nelson Mandela and Clinton in addressing the Labour Party conference on Wednesday. The subject once again will be Africa, and more specifically the three issues that currently dog the continent's destiny: Aids, unpayable debts, and unfair trade. Issues that Bono has made his own, and that he, more than any other global icon, including Mandela, has brought to world attention in recent years.

'I believe that Bono has used his celebrity status for more good than anyone who has ever used their celebrity for any cause,' says Jim Leach, the moderate Republican congressman for Iowa. 'He has, in effect, tackled the biggest issue of our time, which is not war, but disease control: 20 million people have died of Aids in Africa, 40-60m are affected ... he has used his position to rivet the world's attention to this pandemic. That has taken real dedication and a commitment of the kind we are not used to expecting from even the most concerned celebrities.'

Read the rest of The Observer profile here.