Mohamed ElBaradei, the former head of the United Nations nuclear watchdog, has received a hero's welcome upon his return to Egypt.
ElBaradei, who arrived in Cairo on Friday, is seen as a potential presidential candidate and has repeatedly called for democratic change in Egypt since stepping down from his UN post.
One local opposition newspaper had printed flight details for his arrival under the headline "Baradei Returns" to rally people to meet him at the airport.
Ahead of his arrival, there were media speculation that the authorities could ban public receptions for him.
Two members of opposition group the April 6 Movement have already been arrested for organising a reception for ElBaradei and distributing leaflets encouraging people to attend, Egyptian media reported.
Amr El-Kahky, Al Jazeera's correspondent in Cairo, said his return has caused a political stir in Egypt.
"Hundreds of people gathered at the airport ... ElBaradei insisted on acknowledging his supporters but he couldn't make it through the crowds.
"Officials were playing down ElBaradei's arrival ... whether his return will be like a snowball or the regime will stay as it is, that's yet to be seen," he said.
Since November, ElBaradei has in several newspaper interviews pointedly refused to rule out standing in next year's presidential election as a challenger to Hosni Mubarak, the incumbent.
But ElBaradei has made his candidacy conditional on the unlikely prospect of wide-ranging institutional and political reforms to ensure a clean election.
Electoral law also requires him to be a member of an authorised political party, a condition that he does not currently fulfil.
Abdullah al-Ashaal, a former Egyptian diplomat who lectures in political science at the American University in Cairo, said ElBaradei's popularity was a "test" for Mubarak.
"It is the biggest threat to President Mubarak since he came to power ... ElBaradei has come to be a symbol now, a symbol to challenge that dinosaur," he told Al Jazeera.
"I think that this will be very interesting to see how much ElBaradei can do with all the Egyptian people around him ... This is a test for the regime."
Mubarak, who has ruled for three decades, has not said if he plans to run in 2011 but most Egyptians speculate that if he bows out he will seek to hand power to his son Gamal.
Both men deny any such plans.
ElBaradei has found online the support of thousands of people who are tired of Mubarak's rule.
AbdulRahman Yusuf, who runs a Facebook social networking site group called "ElBaradei for Presidency of Egypt 2011", said the group would work in the streets and over the internet to build backing for ElBaradei.
"Our aim is to bring together activists on the ground who can galvanise a popular base through peaceful means," he said.
"We do not seek to whip up a frenzy. We seek amendments to the constitution."