J Christopher Stevens, who has been killed in an attack on the US consulate in Benghazi, was a veteran diplomat who had been in the post of Ambassador to Libya since 22 May.
President Barack Obama described Mr Stevens as "a courageous and exemplary representative of the United States".
"Throughout the Libyan revolution, he selflessly served our country and the Libyan people at our mission in Benghazi... His legacy will endure wherever human beings reach for liberty and justice," Mr Obama said.
In a statement to a US Senate committee after his nomination as ambassador, Mr Stevens wrote of his "extraordinary honour" at being selected for the post.
Mr Stevens had held two previous posts in Libya, as deputy chief of the US mission between 2007 and 2009 and then as envoy to the Transitional National Council (TNC) during the Libyan uprising in 2011, according to the US state department.
Secretary of State Hillary Clinton said the Mr Stevens "won friends for America in distant places and made other people's hopes his own".
"He risked his life to stop a tyrant and gave his life trying to build a better Libya," she said.
"The world needs more Chris Stevenses," Ms Clinton said, adding that she had spoken to the ambassador's sister and told her that he would be remembered "as a hero by many nations".
In an article in a state department publication, Mr Stevens described arriving in Benghazi in April 2011 in a Greek cargo ship to make contact with the TNC.
Mr Stevens and his team facilitated "non-lethal military assistance" to the TNC, the article said.
In diplomatic cables leaked by the Wikileaks site, Mr Stevens had earlier described Col Muammar Gaddafi as "notoriously mercurial" and wrote that he could be an "engaging and charming interlocutor".
A speaker of Arabic and French, Mr Stevens had also been posted elsewhere in the region during his career, including Jerusalem, Damascus and Cairo.
He had worked in several posts in Washington, including at the state department's Bureau of Near Eastern Affairs.
Born and raised in northern California, Mr Stevens had been an international trade lawyer in Washington DC before joining the US Foreign Service in 1991.
In a video posted on YouTube after his appointment, Mr Stevens talked of his experiences as a Peace Corps volunteer in North Africa after graduating from the University of California, Berkeley.
Mr Stevens speaks in the video of the two years he spent as an English teacher in the Atlas Mountains region of Morocco and how he "quickly grew to love" the area.
On a website run by ex-Peace Corp volunteers, Mr Stevens was described as the "quintessential diplomat" by Joan Mower, who was in his training class at the Foreign Service.
Mr Stevens had "an unflappable personality... He listens to people," Ms Mower said.