Liberal opposition leader Mohamed ElBaradei, who was named as Egypt's new prime minister on Saturday, is a former head of UN nuclear watchdog the International Atomic Energy Agency.
The Tamarod campaign behind the protests that toppled Islamist president Mohamed Morsi on Wednesday said after talks with interim president Adly Mansour that ElBaradei, who returned home in February 2010 after retiring as IAEA chief, had been picked as premier.
Tamarod had already nominated him to represent the movement in transition negotiations with the military.
ElBaradei is close to the liberal pro-democracy movement that spearheaded the overthrow of Hosni Mubarak's 30-year rule in February, 2011.
In January 2012, his decision to quit the race for the presidency was seen in Egypt as a slap in the face for post-Mubarak military rulers and one depriving liberals of a key champion.
In late June this year, he urged Morsi to resign after one year in office for the sake of national unity, ahead of record opposition-backed rallies calling on the Islamist leader to step down.
"For Egypt's sake, I call on President Mohamed Morsi to resign and give us the opportunity to begin a new phase based on the principles of the revolution, which are freedom and social justice," ElBaradei said last month.
"I would like to call on President Mohamed Morsi and his Muslim Brotherhood to respond to the cries from all over Egypt," he added at a conference aimed at drawing up a plan for a post-Morsi order.
Rather than join a political party, the 71-year-old ElBaradei created a movement of his own to act as an umbrella for a range of opposition groups -- the National Association for Change.
ElBaradei, who is untainted by the allegations of corruption that surrounded Mubarak's regime, was however criticised by opposition groups for spending too much time abroad and being out of touch with Egypt's reality.
His 12 years as the public face of the UN nuclear watchdog nonetheless earned him respect at home, where he was awarded the country's highest honour, the Nile Shas, in 2006.
Ahead of the 2003 US-led invasion of Iraq, he won admiration around the world and infuriated Washington by challenging claims that Saddam Hussein was hiding a secret nuclear programme.
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No nuclear weapons were later found by US-led forces.
ElBaradei is not a noted orator, but has earned a reputation for speaking his mind. He has lambasted what he calls the double standards of countries that have nuclear weapons but prevent other countries from obtaining them.
He was born on June 17, 1942, in Cairo, where his lawyer father headed the bar association, a position that sometimes put him at odds with then Egyptian strongman Gamal Abdel Nasser.
Following in his father's footsteps, ElBaradei earned his law degree at the University of Cairo in 1962.
Two years later, he joined the diplomatic service and was assigned to the missions in Geneva and New York, where he earned a doctorate in international law and later taught.
He has written that his New York years were among the most formative, helping to broaden his world view.
As special assistant to the foreign minister, ElBaradei served on the negotiating team at the historic Camp David peace talks that led to Egypt's peace treaty and diplomatic relations with Israel.
ElBaradei began his UN career in 1980, and was sent to Iraq in the wake of the 1991 Gulf war to dismantle Saddam's nuclear programme.
In 1997, he was chosen as head of the IAEA, a role that made him a household name worldwide and led to confrontations with Washington, first over Iraq and later over Iran.
When Washington claimed Iraq was buying uranium in Africa, ElBaradei dismissed the evidence before the UN Security Council as fake.
The Washington Post reported that ElBaradei's Vienna telephone was bugged by the US Central Intelligence Agency.
In 2005, ElBaradei and the IAEA won the Nobel peace prize for their efforts "to prevent nuclear energy from being used for military purposes and to ensure that nuclear energy for peaceful purposes is used in the safest possible way".
ElBaradei, who is married to kindergarten teacher Aida Elkashef, has a son, Mostafa and a daughter Laila.