Warren Buffett likes to play bridge and the ukulele

It is the first time a biography will have be written with his co-operation, and deal is worth $7m (�4m), AP says.

Mr Buffett, known as the Sage of Omaha, is the world's second richest man, said by Forbes to be worth $40bn (�22.6bn).

The book, which will focus on his investment strategy, is likely to be called The Snowball: How Warren Buffett Collected Friends, Wisdom and Wealth.

Homespun style

The book will be written by Alice Schroeder, formerly an analyst at Morgan Stanley, where she first came into contact with Mr Buffett.

Although it is claimed it will reveal the secrets of his successful investment strategy, the contract was negotiated with the writer, not with the investment star famous for his homespun style.

Warren Buffett Wears sweatshirts in spare time Enjoys burgers, fries and cola Plays bridge and ukulele Former night school teacher

"Our deal is with her. She is the author," Bantam president and publisher Irwyn Applebaum told AP through spokeswoman Barbara Burg.

The returns Mr Buffett has generated have won him a loyal investor base and turned many of his followers into multi-millionaires.

Had you given Mr Buffett $10,000 in 1965, by 1999 that nest egg would have been worth more than $50m.

'Unprecedented access'

In 1956 Mr Buffett built a partnership of four relatives and three close friends - he now controls a holding company worth $100bn (�56.7bn).

Shares in his investment firm Berkshire Hathaway - which owns insurance, soft drink, confectionery, furniture, restaurant and carpet firms - are currently trading at $83,000 each.

Mr Buffett is not one for fads and has built his investment empire on the maxim that it is better to identify a good investment and hold it for a long time, rather than jump in and out of positions.

The world's second-richest person behind Microsoft founder Bill Gates, he famously sat out the whole internet boom.

Dell says the new book will be based on the "thousands of hours" the writer spent with Mr Buffett and on "unprecedented access to his files, friends and associates".