Microsoft Corp. co-founder Bill Gates, who made the company one of the world's most valuable technology firms, stepped down from the board on Friday to focus on philanthropic works related to global health, education and climate change.

Gates also stepped down from the board of Warren Buffett's Berkshire Hathaway Inc., where he has served since 2004.

The billionaire and his wife Melinda run one of the world's largest charities, the Gates Foundation, which has billions in assets and funds global health programs to combat disease and poverty.

Gates quit his full-time executive role at Microsoft in 2008 and remained as chairman of the board till 2014. Since then he has been a board member.

"It's been a tremendous honor and privilege to have worked with and learned from Bill over the years," Chief Executive Officer Satya Nadella said.

With the departure of Gates from Microsoft Board, it will now consist of 12 members, the company said.

Berkshire said former American Express Co Chief Executive Officer Kenneth Chenault has been nominated to the conglomerate's board of directors, replacing Gates.

The change was disclosed in Berkshire's annual proxy filing, ahead of its scheduled May 2 annual meeting.

Chenault, 68, led New York-based American Express from January 2001 to February 2018, and became one of the most prominent black CEOs in corporate America.

Berkshire knows Chenault well, having long been American Express' largest shareholder, and ending 2019 with an 18.7% stake in the travel and financial services company.

Gates, 64, has known Buffett since 1991 and been a Berkshire director since 2004, but now devotes most of his attention to philanthropy, including the Bill & Melinda Gates Foundation.

He is also the world's second-richest person, worth $103.6 billion according to Forbes magazine. Buffett ranks fourth, at $76 billion.

In Friday's filing, Berkshire also recommended that shareholders reject a proposal by four New York City public pension plans that lists of outside candidates for board seats include "qualified female and racially/ethnically diverse candidates."

Three members of Berkshire's 14-person board are women, and Chenault would become the only black director.

Berkshire said it has for decades "forcefully" preferred directors with integrity, business savvy, an owner-responsive mindset and a deep personal interest in the company.

It said Cnehault emerged as a "standout and unanimous choice" after its governance committee reviewed 23 candidates for board seats last year.

Berkshire said it may choose future board members from that list, noting that four directors, including Buffett, are between 89 and 96 years old.

The proxy filing also detailed compensation for top Berkshire executives in 2019.

Buffett was awarded $374,773, including his usual $100,000 salary plus $274,773 for personal and home security services.

Vice Chairmen Greg Abel, 57, and Ajit Jain, 68, who respectively oversee Berkshire's non-insurance and insurance operations, were each awarded $19 million, up from $18 million in 2018.

Buffett sets compensation for Abel and Jain, who many investors view as top candidates to eventually succeed him as CEO. Berkshire does not grant stock options.

While Berkshire's annual meeting will be held as scheduled, the coronavirus pandemic prompted Buffett on Friday to cancel other shareholder events in Omaha for the May 1-3 weekend.