The social network’s CEO, Mark Zuckerberg, announced the board appointment on Thursday and said he had been “trying to recruit Ken for years.”

“He has unique expertise in areas I believe Facebook needs to learn and improve — customer service, direct commerce, and building a trusted brand,” Zuckerberg wrote in a Facebook post. “Ken also has a strong sense of social mission and the perspective that comes from running an important public company for decades.”

Chenault retired in October after a 16-year stint leading American Express, and was the credit card company’s first black CEO and one of the few black leaders among Fortune 500 companies. With him no longer leading American Express, the Fortune 500 has only three black CEOs.

Shortly after announcing his planned retirement, Chenault described the lack of African-American CEOs leading Fortune 500 companies as “a real problem” that is “embarrassing for corporate America.”

In October, Facebook chief operating officer Sheryl Sandberg told the Congressional Black Caucus that the social network was looking to add an African-American board member. The caucus has criticized Facebook and other technology giants for failing to fix the lack of diversity in Silicon Valley, where minorities and women are underrepresented, especially in high-paying roles and executive leadership positions.

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Civil rights activist and Rev. Jesse Jackson also criticized Facebook in June during a shareholder meeting for failing to add any African-Americans, Asians, or Latinos to its board.

“Ken and I have had dinners discussing our mission and strategy for years, and he has already helped me think through some of the bigger issues I’m hoping we take on this year,” Zuckerberg said Thursday.