Bono can hold the undivided attention of a sold-out stadium. When he works a much smaller space, say in the White House, Downing Street or the Vatican, he rules that room with those who rule the world. When he put his sunglasses on the Pope, that picture became iconic because of his glasses, not because of the pontiff. How? Why? His father told him never to have dreams because he didn’t want him to be disappointed, which encouraged him to dream even bigger. But that’s only part of the long answer.

Contrariness, caring deeply, ridiculousness, egomania, it’s all there. There’s never been a rock star who wielded so much power. There’s nobody in power who doesn’t take his call. During the writing of this piece, there’s nobody in power who doesn’t return my call within 24 hours. Few people say no to Bono, whether it’s Blair, Clinton, Bush. And Bono didn’t say no to Obama when he asked U2 to play at his inauguration concert.

There’s no shortage of Bono jokes. Quite a few of them begin: “What’s the difference between Bono and God?” “Bono thinks he’s God, but God doesn’t think he’s Bono”; that sort of thing. And there’s no shortage of criticism at his ubiquity: when U2 released their album in March with a concert on top of BBC Broadcasting House in London, listeners were furious that the band seemed to be on almost every BBC radio station. Does he ever stop?

Not often. Up early. Sometimes 13 meetings a day. Late nights. Having shadowed him for over six months, I’ve seen how stretched he is and how much he can do. There are many Bonos all in one: the rock star, the activist, the writer, the family man. It’s tough to get him alone. He’s usually only interviewed — and always with the band. It’s even tougher to get him to talk about himself. But after years of interviews with U2, this time he agreed to let me look closely at what it means to be Bono — taking me with him as he made an album; met senior politicians; made speeches; chilled out with friends and, unprecedented for him, taking me home.

This journey begins in October 2008 at the Women’s Conference, Long Beach, California.

I have seen Bono shrink a stadium, make it intimate. But only as a singer in a rock band. As a speaker here, it’s pretty much the same thing. He follows Billie Jean King and Gloria Steinem, who had 14,000 women — the groomed, the earnest, the curious and the militant — roaring with approval. They’re a hard act to follow, but he topped it. “My name is Bono and I’m a travelling salesman. I come from a long line of travelling salespeople on my mother’s side. Sometimes I come to your door as a rock star selling melodies. Sometimes I come as an activist selling ideas of debt forgiveness.” He flatters and cajoles. He says: “Africa’s our neighbour. When it burns, we smell the smoke. It stings our eyes, it sears our conscience, but maybe not as much as it should. We accept it, men especially. A lot of men have developed an ability to live with this absurdity. Most women haven’t.” Everyone is swept up.

He talks about when he first went to Africa and a child was dying in his arms; the look in that child’s eye of innocence and no blame. He says that’s when he became that thing he despises most: a rock star with a cause. Then he talks about how 20 cents can provide life-saving drugs and how you can do this by buying a Red T-shirt. (Red is the organisation he set up so big brands like Gap, Armani and Apple give up to 40% of their profit directly to the Global Fund. To date it has raised over $130m.) It was a 40-minute speech but we felt scooped up, like at a rock concert.

Backstage, there’s Maria Shriver, the conference founder, scion of the Kennedy clan and married to Governor Arnold Schwarzenegger. She looks big-haired, well put together. A purple Alaïa suit skims her, accessorised with pink rosary beads that signal quirky, heartfelt. I told her she looked gorgeous. She looked at me blankly, somehow insulted, and looked at Bono with a “Who is this woman you brought here?” look. Bono refused to acknowledge the moment. He moves on. On stage he’d called Shriver a lioness, a term he uses for powerful women. Later on that’s what he called Nancy Pelosi, speaker of the House of Representatives and arguably the most powerful woman in America. It seemed to make her purr.

December 2008: Olympic Studios, Barnes, London, a few days before the album No Line on the Horizon is finished. I’m sitting next to Bono in the canteen. He’s eating spicy spaghetti and wearing a soft grey cashmere jumper flecked with little metal bits. Hard and soft, I observe. “Yes, that’s me,” he says. I once told him he wears his inside on his out. “You did, didn’t you?” He has the memory of an elephant for stupid minutiae and life-saving facts. But some things are too deeply buried to remember. The first time I met him, we talked about his mother. She died when he was 14, yet he has few memories of her. He recalls her chasing him with a cane and laughing. He recalls his dad at the top of the stairs doing DIY with an electric drill. The drill was screaming. It was going to drill him to death. He remembers his mother convulsed with laughter. Laughter and danger got mixed up in his head.

Bono, 49, has always loved to embrace a contradiction. In his life and lyrics he is always mixing God and sex, poverty and romance. He is supersensitive, but a bulldozer, relentless when he wants something; self-conscious yet without fear. Sometimes saintly, never a monk. Hard and soft Bono lives in two different worlds, exposing himself to two different standards of judgment. Artistically, he is painfully self-critical. When U2 started, he would ask how many people were at the gig. If it was 400 and the venue held 450 he would worry about the 50 who didn’t come. He’s still like that, although the venues are now holding tens of thousands. Yet he can walk into a room on Capitol Hill knowing what he’s asking for is likely to be shot down. The man who pursues success so relentlessly has rewired himself to accept failure as part of his course.

Paul McGuinness, U2’s manager, often referred to as the band’s fifth member, agrees. “He’s a bundle of contradictions, a spoilt-rotten rich rock star who became successful from his own talent. He didn’t trick anyone. He enjoys life to the full, but he does a lot of good. He has difficulties; one day he’ll win a Grammy for album of the year, the next he’s called a terrible hypocrite, a force for bad. Yet the organisations that support his activism are sophisticated. Red is extremely successful. As is One [his global advocacy and campaigning group].”

Earlier that day in December, Bono had a One meeting in London with a video link to the organisation’s office in Washington, DC. They talked about plans for 2010: a World Cup campaign for mosquito nets and education. They talked about what’s going to happen when Obama has to make tough decisions and makes himself unpopular. Could they still count on him? What Republicans should they now work on? How to encourage Cameron on side? How Sarkozy has let them down by not paying what he had promised. Bono jokes Carla is going to make Sarkozy change; he says he’ll have to call her and say: “I know who you’re sleeping with.”

Explore Music

• CD Reviews

• Live Reviews

• Classical

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010