Ayman al-Zawahiri has been named as the new leader of al-Qaeda, following the death of Osama Bin Laden in May.
The Egyptian militant is known to be highly intelligent, but is said to lack the charisma of Bin Laden.
Zawahiri has regularly appeared in audio and video messages since becoming involved with al-Qaeda. Here are some of his key statements.
All these sins and crimes committed by the Americans are a clear declaration of war on God, his messenger and Muslims.
The ruling to kill the Americans and their allies - civilians and military - is an individual duty for every Muslim who can do it in every country in which it is possible to do it...
We, with God's help, call on every Muslim who believes in God and wishes to be rewarded to comply with God's order to kill the Americans and plunder their money wherever and whenever they find it.
Tell America that its bombings, its threats and its acts of aggression do not frighten us. The war has only just begun.
I congratulate the Muslims on Islam's victory in Iraq. I said more than a year ago that the Americans' departure from Iraq is only a matter of time.
[President George W] Bush, you must admit that you have been defeated in Iraq and that you are being defeated in Afghanistan and that you will soon be defeated in Palestine, with the help and strength of God.
[Muslims should] attack the interests of the Jews and the Americans. Select your targets, collect the appropriate funds, assemble your equipment, plan accurately and then charge towards your targets. There is no place today for those who claim that the battlefield with the Jews is limited to Palestine. Let us hit their interests everywhere.
The first signs of victory have already appeared. Soon, Iraq will become a fortress of Islam, from whence the squadrons and regiments tasked with liberating the Al-Aqsa mosque [in Jerusalem] will burst forth, with the help of Allah.
Iraq today is the most important front line for the participation of our Islamic nation against the forces of the crusader Zionist invasion. Due to this, providing assistance to the mujahideen in Iraq - at their head, the Islamic State of Iraq (ISI) - is one of the most important duties required of the Islamic nation today.
You were born to a Muslim father, but you chose to stand in the ranks of the enemies of the Muslims, and pray the prayer of the Jews, although you claim to be Christian, in order to climb the rungs of leadership in America.
In you and in [former US Secretary of State] Colin Powell, [former US Secretary of State Condoleezza] Rice and your likes, the words of Malcolm X concerning "House Negroes" are confirmed.
America, the criminal, trespassing crusader, continues to be the same as ever, so we must continue to harm it in order for it to come to its senses.
In France, the pioneer of secularism, there is an overt and shameless war on hijab and niqab. What France is doing... should prompt us to hold on to our true religion in face of their deviant ideologies.
My Muslim sisters, hold on to your hijab, even if it would cost you your money, education and jobs. You are mujahedat [female holy warriors] in the most important battlefield.
The primary concern of the ruling class in the government and army of Pakistan is filling their domestic and foreign bank accounts with dollars, and as far as they are concerned, Pakistan and its people can go to hell.
The Muslim Turkish people must confront the behaviour of their government, which is participating in the Muslim-killing campaign in Afghanistan. The same holds true for the government of Pakistan.
We must continue on [Bin Laden's] path of jihad to expel the invaders from the land of Muslims and to purify it from injustice.
The man who terrified America in his life will continue to terrify it after his death. You will continue to be troubled by his famous vow: You shall not dream of security until we enjoy it and until you depart the Muslims' lands.
America is not facing an individual or a group, but a rebelling nation, which has awoken from its sleep in a jihadist renaissance.