Warren Buffett, the world's second-richest person, is donating about $37 billion - more than 80 percent of his fortune - to foundations run by his friend Bill Gates and by the Buffett family. The move is the biggest-ever single act of charitable giving in the United States.
Sunday's announcement by Buffett, 75, comes just days after Microsoft Chairman Gates said he would move away from his day-to-day role at the software giant to focus more on charity work, and highlights the close friendship of the world's two richest men.
Gates, 50, is a bridge partner of Buffett's and a director of Berkshire Hathaway, Buffett's investment firm. Buffett serves on the board of the Washington Post Co with Gates' wife Melinda.
In a letter to the Bill and Melinda Gates Foundation, Buffett, said he will set aside 10 million shares of Berkshire class B common stock for the foundation. Based on the stock's per-share price of $3071.01 as of Friday, the total amount for the Gates foundation comes to about $30 billion.
That is the largest commitment to a philanthropic cause ever made by one person in the United States, said Stacy Palmer, editor of the Chronicle of Philanthropy.
"Even if you look at what (John D.) Rockefeller and (Andrew) Carnegie gave historically - even if you do it in today's numbers, it doesn't come close to that," she said.
The Gates foundation is one of the world's richest philanthropic organisations. It has committed millions of dollars to fighting diseases such as malaria and tuberculosis in developing countries, and to education and library technology in the United States.