Pepsi and crisp breakfasts and a mistress sanctioned by his wife ... Welcome to the strange life of the world's richest man

It was the simple, ordinary life of a megabillionaire.

As always, the high-flying investment guru Warren Buffett was accompanied at official functions by his wife Susie, their routine carefully orchestrated like everything in his day.

But when he left the office at 5.30pm, the ordinariness abruptly ended. The woman he returned to was not his wife but Astrid Menks, with whom he had lived since 1978.

He has described the unusual triangular arrangement like this: 'Susie put me together and Astrid keeps me together. They both need to give, and I'm a great receiver, so it works for them.'

A strange answer, but - stranger still - Susie and Astrid appeared to be friends. And it was Susie Buffett who set up the relationship.

Ball park figure: Warren Buffett playing baseball

Buffett was this year named the world's richest man, overtaking Bill Gates with a £35billion fortune, and in the midst of the American financial meltdown he has invested billions in two major companies: Goldman Sachs and General Electric.

But the man dubbed the Sage of Omaha is also famous for his frugality - and his eccentricity.

Even his attitude towards his biographer was unconventional: 'Whenever my version is different from somebody else's,' he told her, 'use the less flattering version.'

Buffett was born in 1930, ten months after the stock market crash of 1929.

Politics, money and philosophy were acceptable topics for the dinner table at home: his father had been a stockbroker in Nebraska and later a Congressman.

Feelings, however, were off-limits. Nobody in the Buffett household said 'I love you', or tucked the children into bed with a kiss.

When in a rage, his mother, Leila, would verbally lash the children, saying their lives were easy compared to her sacrifices, that they were worthless, ungrateful and selfish.

She never stopped until he and his sister Doris 'just folded' and wept helplessly.

Warren took to school immediately, loving anything involving numbers. By the time he was 15, he had amassed $2,000 (about £10,000 at today's money) from delivering newspapers, which he to invested in a shop and a farm in Nebraska.

At business school in Pennsylvania and then Columbia University in New York he was known for his tatty clothes and social ineptitude, but that didn't put off a round-cheeked brunette called Susie Thompson.

She soon detected the vulnerability beneath the surface. All that confident chatter about stock markets was wrapped around a fragile, needy core.

'I was a mess,' he said. 'It was incredible the way Susie saw through to some of that.'

They married while Buffett was working for his father's stockbroking firm, where by the end of 1951 he had made thousands from dealing.

But on his wedding night he ate fried chicken at a tiny diner in Nebraska.

Susie quickly assumed a motherly role. Buffett said: 'I needed her like crazy. I was happy in my work, but I wasn't happy with myself.

'She literally saved my life. She resurrected me. She put me together. It was the same kind of unconditional love you would get from a parent.'

Mainstay: Buffett's first wife, Susie

Although their model of wedded life was typical of the time - he made the money, she covered the domestic front - their arrangement was extreme.

Susie devoted herself to fulfilling her husband's few but specific requirements: Pepsi in the refrigerator, a light bulb in his reading lamp, some indifferently cooked version of meat and potatoes for dinner, popcorn in the cupboard.

He also needed help getting dressed, and in dealing with people and hugs.

Buffett had never been taught to look after himself and had no interest in his appearance. She even cut his hair because he was afraid to go to the barber.

Their first child, Susan, known as Little Susie, was born in 1953 and the following year Buffett took a job with a stockbroker in New York.

When Susie and Little Susie arrived, their apartment was not ready, so the family moved into a room so cramped they had to devise a makeshift crib from a dresser drawer.

On Wall Street, Buffett struck people as a hick, and within their apartment block he had earned a reputation for tightfistedness.

He made a deal with a local newsstand to buy week-old magazines at a discount as they were about to be thrown away. He had no car, and when he borrowed that of a neighbour, he never filled up the tank.

But he flourished, and left New York to start his own firm in Omaha, soon managing more than $1million of investors' money. Arriving home, he would disappear into his study to read and think.

Susie tried to get him involved with their growing family - Little Susie now had two brothers, Howard and Peter - telling him: 'Anyone can be a father, but you have to be a daddy, too.'

But she was talking to someone who'd never had that kind of daddy: when Buffett built himself a large model railway in his attic he forbade the children from playing with it.

Friends joked: 'Warren, those are your children - you recognise them, don't you?' One described Susie as 'sort of a single mother'.

At the beginning of 1964, Buffett was worth nearly $2million, but when his father died that year, he showed no visible sign of grief and criticised Susie for spending too much on the coffin.

Weeks after the funeral, however, bald patches appeared on his head: his hair had fallen out from the shock.

By the time his hair had grown back, Buffett's firm - now worth $37million - had bought an ailing textile mill in Massachusetts called Berkshire Hathaway, later the vehicle for his future investments.

But success had not changed his child-like eccentricity.

He hated vegetables and despised everything green except money. He breakfasted on crisps and Pepsi, ate handfuls of chocolate and popcorn, and chose steaks, hamburgers and the odd sandwich as his main meals.

With such an unhealthy diet, he disciplined himself to keep his weight stable by making out unsigned cheques to his children for $10,000 and declaring that if he didn't weigh 173lb on a specific date, he would sign the cheques. He never signed one.

By 1969, when Susie was spending less time at home, going to jazz clubs and travelling, his fortune was big enough for him to buy a local newspaper, the Omaha Sun.

The paper made him crave entry into publishing's big league, and that opportunity came in 1971 when he met Katharine 'Kay' Graham, publisher of the Washington Post.

The third woman: Washington Post publisher Katharine Graham, pictured with Princess Diana at the White House in 1996

Two years later, Buffett had accumulated a five per cent stake in the Post, and Kay began taking him seriously: it was the start of a mutually supportive relationship.

Kay tended to freeze in front of crowds, something he understood from his teenage years, so he coached her. He was genuinely fascinated by Kay and her social life.

Buffett joined the Washington Post board in 1974, and enjoyed giving Kay the sort of support Susie had offered him: 'I really wanted her to feel better about what she was doing. Basically, I enjoyed trying to build her up.'

As Buffett began to be seen out with Kay, she made it her job to give him some polish: 'Kay tried to upgrade me a little - it was very funny. She worked so hard to sort of remould me, but it didn't work.'

Some foibles were indeed beyond reform. Kay's chef found it a challenge cooking for a man whose idea of a feast was a half-gallon of chocolate-chip ice cream.

Buffett has said: 'I like eating the same thing over and over and over again. I could eat a ham sandwich every day for 50 days in a row for breakfast.'

By now he was spending so much time in Washington that he began keeping a spare set of clothes in Kay's guest room.

Meanwhile, Susie was depressed about her marriage and believed Kay was an interloper pursuing her husband.

In the hot rush of a midlife romance, she let herself be seen around Omaha with John McCabe, her tennis coach.

However, Kay, a flirtatious 59-year-old, was spotted tossing the 46-year-old Buffett her door key at charity events and the two were seen together ever more often in public. By early 1977, gossip columnists had taken note.

Friends, though, observed that the pair had 'zero chemistry'. Whatever romantic elements the relationship may have had initially, at heart it was a friendship.

At 47, Buffett was worth $72million and ran a company valued at $135million, while Susie was doing charity work and trying to establish herself as a singer.

She was also spending a lot of time in San Francisco, and installing her tennis coach in a separate apartment.

It was around this time that Susie struck up a friendship in Omaha with Astrid Menks, a restaurant maitre d' whose Latvian parents arrived in America when she was five.

Small-boned, fair-skinned with ice-blonde hair, she had a Nordic beauty with a subtle hard-knocks edge.

At times she looked even younger than her 31 years. Susie asked her friend to look in on Buffett and cook an occasional meal for him. It was then that, while insisting she was not seeking a divorce, Susie suggested to Buffett that with the children grown up, it was time for her to spread her wings; to have a place of her own in San Francisco. She simply wanted to surround herself with art, music and theatre.

Buffett was devastated. He wandered aimlessly around the house, barely able to feed and clothe himself. He called Susie daily, weeping.

'It was as if they couldn't live together and they couldn't live without each other,' one friend said.

Buffett later admitted: 'It was preventable. It shouldn't have happened. It was my biggest mistake.'

The helper: Astrid Menks, above, was picked by Buffett's wife Susie to look after him

As requested, meanwhile, Astrid phoned him and called round. Arriving at the door to cook a meal, she found a cave filled with books, newspapers and annual reports.

Buffett, incapable of functioning without female companionship, had been reduced emotionally to an 11-year-old boy. He needed feeding; his clothes were unkempt.

Astrid was the least pushy woman imaginable but when faced with this problem, she took control.

By early 1978, with encouragement from Susie, Astrid was cooking and caretaking. Gradually, however, the relationship became something more as Buffett began to accept that Susie wasn't coming back.

Susie herself was shocked. This wasn't what she had in mind when she told her husband they both had needs. In her mind, Warren's dependence on her was absolute; how could he need a relationship with anyone else?

It might have been predicted. Astrid did all that was required: doing the laundry, taking care of the house, buying the Pepsi, giving him head rubs, cooking the meals and providing companionship. She never told him what to do and asked for nothing in return.

As Susie adjusted to the shock, she came to accept the situation, which did make her life easier. Buffett was perfectly open about living with Astrid, merely saying: 'If you knew the people involved, you'd see that it suited all of us quite well.'

Astrid accepted that Buffett would never marry her, so she tolerated being called his housekeeper and mistress, while Susie accompanied him to social and business events.

Buffett said: 'Astrid knows where she fits with me. She knows she's needed. That's not a bad place to be.'

He appeared to be getting the best of both worlds, but he couldn't defend himself against the impression that he had driven his wife away through his relationship with Katharine Graham.

Kay, in turn, handled the situation by acting as if Astrid didn't exist, except for calling her once to ask how to work her video recorder.

Susie and Astrid were perfectly comfortable with each other: Astrid even went to San Francisco to visit Susie, who was by now grateful to the younger woman for making her life easier.

The year 1985 was extraordinary. In a single week Buffett made more than £180million from just one investment.

At 55, he was now a billionaire, yet he drove an eight-year-old Cadillac and lived in his original, modest house. He bought Coca-Cola shares although he drank Pepsi; he bought a jewellers although he had no interest in appearances.

His status as one of the super-rich meant he was now no longer so dependent on Kay for A-list invitations, and she no longer needed him as a regular escort, for their mutual obsession had cooled.

After her death in 2001, Buffett did not speak at her massive funeral, something he later regretted: a week later he was heard sobbing with grief.

In 2003 he suffered another blow when Susie was diagnosed with cancer. He always assumed she would be there for him at the end, to calm his terror and ease his suffering when death was approaching.

Susie got through surgery and radiotherapy and was declared clear in 2004.

All three returned to their 'normal' routine: Astrid accompanying Buffett only to the backstage social events while Susie attended the official social events in the role of 'wife'.

Devastated: Warren Buffett at Katharine Graham's funeral with Bill Gates, right

In a television interview, Susie was asked if Astrid took care of her man for her.

'She did, and she takes great care of him, and he appreciates it and I appreciate it ... she's done me a great favour,' Susie said.

But Susie's recovery was short-lived. She died from a stroke later that year.

As the funeral approached, it became apparent to Buffett's daughter, Little Susie, that something else was bothering her father. It dawned on her what this must be.

'You don't have to go,' she told him. Buffett was overcome with relief. 'I can't,' he said. To sit there, overwhelmed with thoughts of Susie, in front of everyone, was too much. 'I can't go.'

But unlike him, hundreds of others did want to grieve for her at some sort of memorial service.

None was ever held. Only the family, a couple of Susie's closest friends, including the singer Bono and his wife, Ali, were invited to the funeral.

Little Susie had met Bono through one of her father's companies and the singer had invited her to join the board of his charitable operation DATA (Debt, AIDS, Trade, Africa). He later became friends with her mother.

At the funeral, the grandchildren wept as Bono sang Sometimes You Can't Make It On Your Own.

Many people, including Susie herself, had questioned how well Buffett could survive without her. His 74th birthday was approaching with its metronomic tick of doom.

He could not escape from grief, even in sleep. All he had ever asked of her was not to leave him and she had promised that she never would.

But gradually, as he passed through the stages of mourning, he brought Astrid into his public life. And in 2006, he announced that he would give £20billion in investments to charities.

Astrid was now Buffett's official companion. Two years after Susie's death, on his 76th birthday, Buffett married her in an unfussy civil ceremony.

Astrid wore a turquoise blouse and white trousers, he wore a business suit. Tears welled from her eyes as he placed a huge diamond solitaire ring on her finger.

Buffett now had one wife, drove one car, occupied one house that hadn't been redecorated in years, ran one business, and spent more time with his family.

A complex man of simple tastes, he now had the life of the man that he had always believed himself to be. But nonetheless, the financial world is still turning for him.