Thomas-Greenfield joined the State Department more than three decades ago, when Black women were even more of a rarity in the U.S. diplomatic corps than they are today.
That makes her the most experienced diplomat of the six people named by Biden for top national security positions on Monday.
Her tenure at the State Department rivals that of previous U.N. ambassadors like Richard Holbrooke, John Negroponte and Thomas Pickering, all of them white men.
Other than secretary of state, the U.S. ambassador to the United Nations is often the most high-profile foreign policy portfolio in a presidential administration.
Thomas-Greenfield's immediate predecessors โ all women โ highlight that dichotomy: Rice, Samantha Power, Nikki Haley and Kelly Craft.