But when you're the richest man in the world, with controlling tendencies, even moments of joyful spontaneity sometimes have to be carefully scripted. It is not cheap. Take Gates's autumn break this year, when he took friends by rail across Montana, Wyoming and Colorado. When the party stopped at a restaurant, a couple of rowdy strangers joined in uninvited and poked fun at the computer-geek. "Hey, aren't you that computer guy Steve Jobs?" they asked Gates playfully, according to The Washington Post, deliberately confusing the Microsoft chairman with his former rival, the founder of Apple Computers. The guests laughed, nervously, at the impertinence of it all. It was later revealed that the chappieswere actually actors, hired to provide some impromptu entertainment. Gates even gave them strict instructions on what to say and do.

It was the most bizarre episode in a carefully managed trip. Gates's guests, including America's second richest man -- Warren Buffet -- were transported across the Rockies in a private train, triggering complaints from rail travellers whose journeys were held up to allow the express to thunder by. In return for the fun, the guests were required to sign confidentiality agreements.

The multi-millionaire Harvard drop-out built the ultimate controlled environment for his family in a 37 million-pound lakeside mansion near Microsoft's Seattle offices. An electronic system adjusts lighting, music and air-conditioning as he moves around the house, while a touch-sensitive pad allows his two-year-old daughter, Jennifer, to conjure up any song or film scene in 30 seconds.

The Observer News Service