Warren Buffett, the billionaire investment guru known as the Oracle of Omaha, is donating about $2.6 billion in stocks to five charities as part of a plan to give away the bulk of his wealth before he dies.

The bulk of the annual donation, about $2 billion, went to the Gates Foundation, the philanthropic organization set up by Microsoft co-founder Bill Gates. Buffett also donated millions to his own foundation and the charitable organizations set up by his three children.

Buffett, the second-richest American and the third-richest global billionaire on Forbes’ lists, has been a leading advocate for philanthropy among the wealthy.

Buffet and Gates launched The Giving Pledge in 2010, encouraging the world’s wealthy to commit to donating 50% or more of their fortunes to philanthropy during their lifetime or after they die.