Mohamed ElBaradei, who has become a leading symbol for democratic change in Egypt, emerged as a bitter foe of the United States when he led the International Atomic Energy Agency (IAEA) between 1997 and 2009.
In 2005, the State Department launched a failed campaign to block the Egyptian lawyer from winning a third term as director general of the IAEA. That same year, the Nobel committee awarded him the Peace Prize.
Between 2003 and 2009, when Mr. ElBaradei oversaw the IAEA's inspections of the Iranian nuclear program, the clashes with the United States and its allies reached a new peak.
"You have to remember what he said. He said he had a moral responsibility as a Nobel laureate to do things that were not normally in the portfolio of a director general. This was his opinion of his responsibility," said Olli Heinonen, a former IAEA weapons inspector who worked closely with Mr. ElBaradei.
In a 2007 interview with the New York Times magazine, Mr. ElBaradei described himself as a "secular pope" who saw his role in international politics to "make sure, frankly, that we do not end up killing each other."
It was this view that led many Western and U.S. diplomats interviewed for this story to conclude that at times Mr. ElBaradei worked as Iran's advocate and not an independent auditor of its nuclear program.
"ElBaradei consistently demonstrated a pro-Iran bias when he was at the IAEA," said John R. Bolton, who worked with Mr. ElBaradei as an undersecretary of state and as a U.S. ambassador to the United Nations.
"The pro-Iran bias was complementary to his anti-American bias," Mr. Bolton said. "I think he was harming the agency and not doing the job that he should have against Iran's nuclear weapons program."
In 2003, Mr. ElBaradei rejected U.S. information on Iraq's procurement of yellowcake uranium in Niger and was an outspoken foe of the Iraq war.
Over time, some diplomats said his Iraq experience led Mr. ElBaradei to pursue gambits to delay the diplomatic censure of Iran at the U.N. Security Council.
"The context was ElBaradei felt very burnt by the Iraq experience," a Western diplomat said. "He thought we were on the war path with Iran, which was the opposite of the truth. He intervened in a very political way on the Iran file, which goes beyond the technical mandate of the director general of the IAEA."
Concerns about Mr. ElBaradei's management of the Iran file came to a head in August 2009, when the Associated Press first reported on a secret file from the agency that documented what the agency's inspectors on the ground considered to be the military aspects of Iran's nuclear program.
As IAEA director, Mr. ElBaradei never allowed his agency to affirm one way or the other in public that Iran was pursuing nuclear weaponry.
Mr. Heinonen said Mr. ElBaradei "would at times use tough language with the Iranians" in private meetings.
"The public reports on the Iranian program did not always use the same tone as what was said in private discussions," Mr. Heinonen said. "But it is up to the discretion of the director general as to how he wants to explain the negotiations and the inspections of Iran's program to the member states."
Mr. Bolton said, in his experience, Mr. ElBaradei would at times alter reports from his inspectors.
"I think he ran cover for Iran," Mr. Bolton said. "He would not face up to the realities that everyone else saw, that Iran had a nuclear weapons program. We know he altered reports by IAEA inspectors."
Michael Adler, an Iran expert at the Woodrow Wilson International Center for Scholars, disagreed.
"It's incorrect to say that ElBaradei suppressed information when he was the director general from the board of governors reports," he said. "If you look at those reports, they document very meticulously and fully the Iranian nuclear program, to the extent they were able to document it."
Today, Mr. ElBaradei has emerged as the opposition's mediator and negotiator with the Egyptian government. Last year, he accepted political support from the Muslim Brotherhood in Egypt and said he would run for the presidency in the 2011 elections if the election laws were amended to allow him to run competitively.
The U.S. ambassador in Cairo, Margaret Scobey, in the past has met with Mr. ElBaradei. Since the major demonstrations began last week in Cairo, the White House has not yet reached out to him, according to a White House official.
Michele Dunne, an Egypt expert at the Carnegie Endowment for International Peace, said Mr. ElBaradei "is putting himself forward as someone who can negotiate between the opposition and the government, but he is not necessarily presenting himself as transitional leader."
A concern for some observers is that Mr. ElBaradei is seen as too close to Iran and the Muslim Brotherhood and may end up being their pawn.
Danielle Pletka, vice president for foreign and defense policy studies at the American Enterprise Institute, said she does not believe the former IAEA director general is a "stooge for Iran."
"Just because someone tells you what you want to hear does not mean they play well at home," she said. "Sometimes, when they play well at home, they are not going to tell you what you want to hear. But this does not make them a bad transitional leader."
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