Billionaire Warren Buffett is donating about $30 billion to foundations run by his friend Bill Gates and by the Buffett family.
The move by the the world's second-richest person is the biggest-ever single act of charitable giving in the United States.
The announcement by Mr Buffett (75) comes just days after Microsoft chairman Mr Gates said he would move away from his day-to-day role at the software giant to focus more on charity work, and it highlights the close friendship of the world's two richest men.
Mr Gates (50) is a bridge partner of Mr Buffett's and a director of Berkshire Hathaway, Mr Buffett's investment firm. Mr Buffett serves on the board of the Washington Post Co. with Mr Gates's wife, Melinda.
In a letter to the Bill and Melinda Gates Foundation, Mr 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.
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.
Mr Buffett took over Berkshire Hathaway in 1965, and has transformed it from a struggling textile maker into a $141.8 billion company with investments in undervalued securities and purchases of well-managed, easy-to-understand businesses.
