Warren Buffett donated roughly $3.17 billion of Berkshire Hathaway Inc. (BRK.A) - Get Report (BRK.B) - Get Report stock on Monday to the Bill and Melinda Gates Foundation and four family charities.

It is the 86-year-old billionaire's largest contribution in his plan to give away his fortune. In 2010, Buffett, Microsoft Corp. (MSFT) - Get Report co-founder Bill Gates and his wife created The Giving Pledge, a project that encourages billionaires to give more than half of their wealth to philanthropy.

The Gates Foundation — created by Bill Gates, a Berkshire director, and his wife — is receiving about $2.42 billion of Monday's donations, Reuters reported. Buffett, a friend of Gates, has given about $21.9 billion to the foundation — which focuses on increasing health, improving education and combating poverty — since 2006.

Buffett's gift on Monday included 18.63 million Class "B" shares of Berkshire, which were valued at $170.25 each at Monday's close.

Although he has donated more than 40% of his holdings in Berkshire, Buffett still owns about 17% of the Omaha, Nebraska-based conglomerate. He has run the company since 1965.

The Susan Thompson Buffett Foundation, named for Buffett's late first wife, as well as the Howard G. Buffett, Sherwood and NoVo Foundations, which his children oversee, also received donations.

There are 170 billionaires that have signed The Giving Pledge. They come from 21 countries and range from people in their 30s to their 90s.

Here are the wealthiest signers, according to Forbes.

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