Christopher Stevens, the US ambassador to Libya killed in Benghazi, was deeply involved in the transition of the North African state and had been US envoy to the rebels who overthrew strongman Muammar Gaddafi last year.
Stevens, 52, who had been ambassador to Libya since May, was one of four Americans who died when Islamist gunmen stormed the Benghazi consulate and another safe house refuge on Tuesday night.
The California-born veteran diplomat, an Arabic and French speaker, served as deputy chief of mission in Tripoli between 2007 and 2009, in the waning years of Gaddafi's mercurial and brutal rule in the oil-rich country.
As the country dissolved into civil war, he was appointed the US envoy to the Transitional National Council, which was coordinating the revolt against Gaddafi, and returned aboard a Greek cargo freighter that docked in Benghazi in April, 2011.
President Barack Obama stressed Stevens's deep ties to Libya and his commitment to helping Libyans build a nascent democracy out of the chaos of war.
"It is especially tragic that Chris Stevens died in Benghazi because it is a city that he helped save," Obama said Wednesday.
Benghazi had been the cradle of the anti-Gaddafi revolt.
"He risked his own life to lend the Libyan people a helping hand to build the foundation for a new, free nation," US secretary of state Hillary Clinton said in a statement.