Born in al-Zaitun district in Gaza City in 1945, al-Zahar graduated with a master's degree in general surgery from Ein Shams University in 1971 and went on to help establish the resistance movement in 1988.
In 1992, Israeli forces expelled al-Zahar and dozens of other Hamas activists, who went into exile in Lebanon.
On 10 September 2003, an Israeli air strike on his home killed his son and bodyguard and injured his wife, his daughter and himself.
Al-Zahar says he is committed to resisting Israeli occupation through military means, but he also believes Hamas has a strong role to play in the Palestinian political process.
His organisation is hoping to participate in parliamentary elections re-scheduled for January 2006.
In recent weeks, US and Israeli officials have said they oppose Hamas participation in the polls. In September, Israeli Prime Minister Ariel Sharon threatened to withhold all cooperation in election preparations if Hamas - considered by his country and the US as a terrorist group - were allowed to run.
Aljazeera.net: Why did the Israelis leave Gaza? Some Israelis have expressed concerns that their pullout will be interpreted as a victory for terrorism.
Mahmoud Khalid al-Zahar: They left Gaza most surely because of Palestinian resistance.
They describe resistance as terrorism. Nobody can deny that the resistance was the only factor that pushed the Israelis to leave the Gaza Strip. It was resistance that put an end to their Zionist dreams, to expand from the Nile to the Euphrates.
They describe Hamas as terrorists because it is we who dealt them severe military losses and wounded their dignity - the dignity of this military power called Israel.
They try to link between us and other terrorist organisations around the world. That is because of their weakness and incompetence in front of Hamas.
Do you expect Israel to withdraw from the West Bank, Jerusalem and other Palestinian lands after Gaza?
We have to push them to leave. It will be honourable for us to participate in the continuation of our resistance to push the Israelis out of these areas and to eliminate the historical crimes committed against the Palestinians and Arabs in Palestine.
What are your plans for facing Israeli attempts to expand settlements in the West Bank, continue building what they call the security barrier and isolating Jerusalem?
We have always believed from the very beginning that any movement without an armed struggle will be a waste of time. When the Palestinians negotiated with the Israelis, they wasted our time and finances.
When we took up arms and launched our armed struggle, we succeeded in less than five years to force the Israelis to withdraw from the Gaza Strip. This fulfilled everyone's dream.
I think we have to benefit from this experience by applying it accordingly to the West Bank and other occupied areas.
Will you go forward with the policy of using suicide bombers?
The world has to understand such operations are not suicide bombings. They are martyrdom operations. These are the most honourable and precious of sacrifices for achieving national and religious goals to end Palestinian suffering. They are justified by our religious scholars, and I think they are very effective in convincing the Israelis that their existence as an occupying power costs them too much.
We are an occupied people; we have to continue our armed struggle by all means to resist occupation.
Will you continue targeting civilians?
In the last intifada, more than one-third of the Palestinians killed by Israeli forces were children and the majority of all casualties were civilians. We are applying the principle [eye for eye and, nose for nose, civilian for civilian].
Moreover, concerning the Israeli people, all of them are highly qualified and trained military soldiers.
What is your relation with the PA and other Palestinian factions?
The PA is not involved in resistance. So how can we cooperate with them on resisting the occupation? We cooperate with the resistance organisations, some of them belong to this faction or that. But with the PA we have no cooperation.
Regarding our relations with the other factions, it is built on the consensus over the resistance programme. Nowadays, all the Palestinian factions and their military wings agree on resorting to an armed struggle to facing the Israelis. The state of calm that exists now is a thing we have agreed upon in Cairo for only one year. At the end of this year, 2005, the Cairo agreement becomes ineffective.
Under these ongoing conditions, what kind of relations do you maintain with the PA and the Palestinian factions?
We have a well-known vision for the Palestinian people concerning the process of working with the Israelis or resisting them. We consider the Israelis our enemy. We will not allow anybody from Hamas to establish a dialogue or working relationship with them. We want to help others to cut their relations with them in the security level and other levels whether in industry or economy.
If the Israelis extended hands for peace with you, would you exchange peace with them?
There is no peace with people who killed our people, occupied our lands and destroyed our homes. How can we reach a peace process with them? We can speak about hudna (truce), long-term ceasefire.
Peace depends on the restoration of our usurped rights. That means the restoration of all the lands occupied since 1948. How can we accept Israel as a legal existence while it occupies our land? We can reach a ceasefire with anybody, but peace with Israel is impossible.
You yourselves, do not think of any kind of dialogue with Israel?
Dialogue is not our intention. Dialogue is a method. What do we get from dialogue? Dialogue for dialogue? That was the big mistake of the PA when they decided that negotiation is the strategic goal.
It is not our strategic goal, but it is a method. Our strategic goal is to liberate our land by all means. What could we possibly discuss by way of negotiations? If they have an agenda that is acceptable for Hamas and we can achieve even a part of our rights, we can discuss that. But this is not our intention.
How do you view Egyptian mediation in the Palestinian-Israeli conflict and between Hamas and the PA?
We appreciate their role as a reconciliatory party. We hope that they may continue their role as the Palestinians are in urgent need of them and their services and facilities, especially as concerns medical assistance.
Who do you blame for the recent clashes in Gaza between PA security forces and members of Hamas?
I think that some in the PA are trying to exaggerate divisions among the Palestinian people in order to justify postponing the elections. These clashes were originally personal disputes which were manipulated into a larger confrontation between Hamas and the PA.
That was intended. We do not want to give them the chance to play this dirty game.
Is there a general feeling in Hamas that the Israelis, Americans and the PA are working to prevent Hamas from entering the elections?
They are afraid of the elections because they know the majority of the people support Hamas.
What is your electoral programme?
We have already told people about our programmes. We have to cut our relations in all levels with the Israelis and to establish and strengthen our relations with the Arabic and Islamic world through the Egyptian and Jordanian channels.
Also, we have to establish an independent economical system and run a very effective educational system. We want to reconstruct Palestinian infrastructure and establish an efficient health services mechanism. All these are known for everybody and it is not the time to speak about the details.
US President George Bush has said he supports Palestinian rights. What is your view on this?
Which rights? Our right is to establish our independent state on our independent land; the historical Palestine. We do not trust America and I think nobody trusts it, especially, after its attacks in Afghanistan and Iraq.
People discovered that America is a big liar when it spoke about the WMD (weapons of mass destruction) in Iraq and after its failure to prove that practically. Anyone who has trusted it has been deceived.
But the US says it is pushing for democracy throughout the world?
There is a big contradiction between the argument of America and what it implements on the ground whether in Afghanistan, Iraq and in Palestine.
They intend to make collaborators with them through a fabricated story of elections. And this is not easy in the Palestinian question.