President Hosni Mubarak, in power for three decades, is facing unprecedented protests from Egyptians inspired by the overthrow of Tunisia's president.
Mr Mubarak has no designated successor. This has fuelled speculation that he is grooming his son, who was the target of criticism by many of the protesters.
The following are some facts about Mr Mubarak:
* Mr Mubarak, 82, was thrust into office when Islamists gunned down his predecessor, Anwar Sadat, at a military parade in 1981. The burly former air force commander has proved a far more durable leader than anyone imagined at the time.
* The president has long promoted peace abroad and more recently backed economic reforms at home led by his cabinet under prime minister Ahmed Nazif, but he has always kept a tight lid on political opposition.
* He has resisted any significant political change even under pressure from the United States, which has poured billions of dollars of military and other aid into Egypt since it became the first Arab state to make peace with Israel, signing a treaty in 1979.
* Mr Mubarak won the first multi-candidate presidential election in 2005 although the outcome was never in doubt and his main rival came a distant second. Rights groups and observers said the election was marred by irregularities.
* He has not said whether he will run for a sixth six-year term in 2011. Officials have indicated he probably will if he can, although questions about his health after surgery in Germany in March make this a constant subject of debate. If he does not run, many Egyptians believe he may try to hand power to his 47-year-old son, Gamal. Both Mubaraks deny such a plan.
* Gamal, unlike his father and Egypt's other presidents, does not have a military background, which analysts say would make it harder for him to establish his authority as president should he seek office.