The man many see as a possible future leader of Egypt received a tumultuous welcome as he flew in to Cairo.
Mohamed ElBaradei, former chief of the United Nations’ atomic energy agency and Nobel peace prize winner, has offered to head a transitional government.
“I wish we didn’t have to go to the street to impress on the regime the need to change. We tried signatures. We tried boycotting the elections. Nothing worked; every demand fell on deaf ears and the young took the credit for going onto the streets and making things happen,” he told a crowd of reporters.
ElBaradei launched a campaign for political change last year.
In June he joined a rally in Alexandria to protest against the death of a man who allegedly died during police torture.
But ElBaradei is not universally popular. Many activists criticise him for continuing to live in Vienna.