Susan Rice was the youngest-ever assistant secretary of state
Barack Obama has chosen one of his closest advisers to work as the US ambassador to the United Nations.
Susan Rice will hold cabinet rank, in a sign of Mr Obama's plan to work more closely with UN member states than the administration of George W Bush has.
Ms Rice worked in the Clinton administration but backed Mr Obama for the Democratic nomination because of his opposition to the Iraq war.
She is also an advocate of tough action to end the killing in Darfur.
She visited Rwanda after the 1994 genocide, while working on the National Security Council.
"I swore to myself that if I ever faced such a crisis again, I would come down on the side of dramatic action, going down in flames if that was required," she said in an interview with the Atlantic Monthly in 2001.
Testifying before the Senate Foreign Relations Committee in April 2007, she supported the idea of military action to force the Sudanese government to halt the massacres.
Ms Rice, a protege of former Secretary of State Madeleine Albright, was the youngest assistant secretary of state in history when appointed by Bill Clinton in 1997, as assistant secretary of state for African affairs.
The New York Times reports that the Clinton camp, during Hillary Clinton's campaign for the Democratic nomination, regarded Ms Rice's support for Mr Obama as a defection.
However, she and Mrs Clinton, as the future US secretary of state, will have to work closely together in the Obama administration.
Ms Rice told the New York Sun in January that she was drawn to support Mr Obama because of his position on Iraq, saying that he had made "the same unpopular choice I had made" despite huge pressure in Washington to support the war.
Growing up, Ms Rice dreamed of becoming a senator for the District of Columbia. She graduated in history from Stanford University, then went to Oxford as a Rhodes scholar, where she completed a D Phil in international relations.
During her stint in the Clinton White House, she was described as "brilliant" but also "authoritarian" and "brash". According to the New York Times, she acknowledges "a certain impatience at times".
Despite having a doctorate, and being an African American, she is no relation of the current Secretary of State, Condoleezza Rice.
Born in 1964, she is married to an ABC producer, Ian Cameron, and has two children.