Billionaire investor Warren Buffett plans to donate a total of $37 billion US to a charitable foundation started by his friend and bridge partner Microsoft chairman Bill Gates.

Buffett, 75 years old and in excellent health, announced Sunday that he intends to donate the bulk of his fortune to the Bill and Melinda Gates Foundation, a charity that has become famous for its work with HIV, malaria and tuberculosis in the Third World, and with education and library technology in the United States.

Warren Buffett, left, Melinda Gates and Bill Gates met Sunday as Buffett made his big announcement.
(Bill and Melinda Gates Foundation, Diane Bondareff)

The donation doubles the value of the Gates foundation, already one of the world's richest charities.

In a letter published Sunday, Buffett praised the Gates foundation for the good work it has already done.

"You have committed yourselves to a few extraordinarily important but underfunded issues, a policy that I believe offers the highest probability of your achieving goals of great consequence," Buffett said.

Buffett also told Fortune magazine that it was better to give his money to an established foundation that was doing good work than expand his own foundation.

"What can be more logical, in whatever you want done, than finding someone better equipped than you are to do it?" Buffett told the magazine.

"Who wouldn't select Tiger Woods to take his place in a high-stakes golf game? That's how I feel about this decision about my money."

Gates responded graciously.

"We are awed by our friend Warren Buffett's decision to use his fortune to address the world's most challenging inequities, and we are humbled that he has chosen to direct a large portion of it to the Bill and Melinda Gates Foundation."

Buffett is one of the world's best-known investors.

He is chief executive officer of Berkshire Hathaway, an investment firm that is involved in insurance, furniture, carpet, jewelry, restaurants and utility firms. He also has major investments in such companies as H&R Block Inc., Anheuser-Busch and Coca-Cola Co.

Those holdings have made Buffett the second-richest man in the world, with assets of about $44 billion US, second only to Gates, who is worth about $50 billion US.

The amount is believed to be the largest philanthropic donation ever made by one person in the United States, dwarfing donations by such stalwarts as John D. Rockefeller and Andrew Carnegie.

Buffett also pledged one million shares to a foundation established for his late wife, and 350,000 shares each to foundations for his three children.

The money will be distributed in annual donations starting next month.