Ayman al-Zawahiri is the new head of the terrorist organization Al Qaeda, assuming the role after Osama bin Laden was found and killed in Pakistan by US forces last month.

Born in Egypt, the 59 year-old Sunni Muslim has been on the Federal Bureau of Investigation's Most Wanted list since 1998, when he was revealed to be behind the bombings of U.S. Embassies in Dar es Salaam, Tanzania, and Nairobi, Kenya that killed hundreds of people. Bin Laden was also named as a mastermind in the attacks.

The FBI profile on al-Zawahiri states:

Al-Zawahiri is a physician and the founder of the Egyptian Islamic Jihad (EIJ). This organization opposes the secular Egyptian Government and seeks its overthrow through violent means. In approximately 1998, the EIJ led by Al-Zawahiri merged with Al Qaeda.

The FBI and the US State Department have set a $25-million reward for information leading directly to the apprehension or conviction of Ayman Al-Zawahiri.

He is now the Number One most wanted man alive.

Al-Zawahiri came from a respectable and religiously strict family in the ideologically-moderate Egyptian town of Maadi. His uncle was the grand imam of Cairo's al-Azhar University, an extremely prestigious position, and his grandfather was the president of Cairo University and founded King Saud University, in Riyadh, Saudi Arabia. Al-Zawahiri was raised under strict Muslim teachings, in contrast to his peers in the area.

Seeds of zealotry were probably planted in al-Zawahiri through his study of radical Islamist literary critic Sayyid Qutb. Qutb was an Egyptian philosopher who believed the country to be impure and in need to spiritual cleansing.

Qutb was arrested for the attempted assassination of Egyptian leader Gamal Abdel Nasser in 1954. Perhaps proving Qutb's influence on the new al-Qaeda leader, al-Zawahiri became a lead organizer for the anti-government organization Egyptian Islamic Jihad, and plotted to overthrow Nasser himself.

Bin Laden and al-Zawahiri: the brains and the bank

While bin Laden was viewed as the leader of al Qaeda and Al- Zawahiri his second in command, their relationship was probably less hierarchical. The Council on Foreign Relations thinks that each of the men influenced one another. Al-Zawahiri is more of an ideological pedagogue and had a direct effect on shaping bin Laden's and al Qaeda's political and religious convictions, while bin Laden, famously from a rich Saudi oil family, was the financial backer of the terrorist organization.

In fact, many counter-terrorism analysts believe that al-Zawahiri was more instrumental in the September 11th attacks than bin Laden.

Zawahiri has a different kind of experience, Pakistani journalist Hamid Mir told the Christian Science Monitor in 2001.

He is not interested in fighting in the mountains. He is thinking more internationally, involved in militancy inside Egypt. He was behind the terrorist attacks on tourists [the 1997 attack in Luxor that left 58 dead]. He is the person who can do the things that happened on Sept. 11.

Al-Zawahiri's experience is much broader than even Bin Laden's, said Egyptian expert Dia'a Rashwan in September, 2001.

His name has come up in nearly every case involving Muslim extremists since the 1970s.

The two men met in the 1980s in Peshawar, Pakistan. Al-Zawahiri was a surgeon for the Red Crescent - an Islamic version of the Red Cross - treating Muslims wounded in fighting with Soviets in Afghanistan. Bin Laden was in the city raising money and guns to fight against the Soviets.

It is believed that al-Zawahiri soon recruited bin Laden for high level positions in his militant organizations, intrigued by bin Laden's fortune and ability to bankroll his operations.

While collaboration between the two before 1998 can only be speculated upon, al-Zawahiri and bin Laden certainly teamed up for the US embassy bombings in East Africa.

The man who was thought to be the brains behind bin Laden's brawn is now in control of the terrorist organization founded by his friend and co-conspirator.

The Sheikh [bin Laden] has departed, may God have mercy on him, to his God as a martyr, and we must continue on his path of jihad to expel the invaders from the land of Muslims and to purify it from injustice, al-Zawahiri said in a video message posted online.

Today, and thanks be to God, America is not facing an individual or a group ... but a rebelling nation which has awoken from its sleep in a jihadist renaissance challenging it wherever it is.

Where is al-Zawahiri?

Similar to Osama bin Laden, al-Zawahiri is believed to be hiding somewhere in Pakistan.

According to the Washington Post, some of the confiscated documents discovered in bin Laden's Abbottabad compound may help US forces locate al-Zawahiri's hiding spot.