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Bill Gates is stepping down from the boards of Microsoft and Berkshire Hathaway to devote more time to philanthropy, he announced Friday. He will continue to serve as technology adviser to Microsoft CEO Satya Nadella.

It is a landmark moment for Gates, the co-founder and former CEO of Microsoft, and a longtime friend and collaborator of Berkshire Hathway chairman and CEO Warren Buffett.

Gates, who started Microsoft in 1975 with Paul Allen, said in a blog post he is stepping down in order "to dedicate more time to philanthropic priorities including global health and development, education, and my increasing engagement in tackling climate change."

Gates said serving on the Berkshire board "has been one of the greatest honors of my career." Of Microsoft, Gates stressed that "stepping down from the board in no way means stepping away from the company."

The news came amid a shuffling of corporate board positions. As Gates announced his departure, Berkshire announced that the board position would be filled by former American Express CEO Kenneth Chenault, who in turn would be leaving the board of Facebook.

Chenault said he was stepping down from Facebook's board "because I have a once-in-a-lifetime opportunity to work more closely with my friend Warren Buffett, the Berkshire Hathaway board and the management team."