Martin Asser BBC News Online

Mohammed Deif has been at the top of Israel's "most wanted" list for years and is thought to have narrowly escaped the Israeli army's efforts to kill him on several occasions.

Although he only took over as Gaza commander of Hamas's military wing in July 2002, Israel holds him personally responsible for the deaths of dozens of people in suicide bombings since 1996.

Arafat has had an ambiguous relationship with Hamas

Israel calls him a mastermind of terror, the man who chooses when and where suicide attacks take place - and sends the bombers on their way.

But unlike Hamas's spiritual leader, the blind, paralysed cleric Sheikh Ahmed Yassin, Mohammed Deif and his Izz al-Din Qassam brigades comrades have always operated in the shadows.

That is why much of Mohammed Deif's history remains obscure, and there has always been doubt about his exact whereabouts when Israeli launched its failed assassination attempts.

Revenge attacks

Piecing together the reports, we can say that Mohammed Deif's mentor was Yehya Ayyash, the renowned Hamas bomb maker known as "the engineer" who led the Qassam brigades until his assassination in December 1995.

Before then, Mohammed Deif took part in operations against Israeli soldiers in Gaza, as part of Hamas's opposition to the then emerging peace process between Yasser Arafat's PLO and Israel's Labor government.

"The Engineer" is still revered by Hamas supporters

But after Ayyash's death, Izz al-Din Qassam took revenge with a series of suicide bombings in Tel Aviv and Jerusalem - apparently masterminded by Mohammed Deif - that had a serious impact on the peace process.

Enjoying considerable grassroots popularity in Gaza, Mr Arafat's Palestinian Authority was unable to fulfil its obligations to Israel under the peace accords by arresting Mohammed Deif.

He was finally taken into custody in May 2000 as a gesture to the Israelis and Americans ahead of the ill-fated Camp David summit.

However, Israel believes that during his confinement he continued to lead the Hamas operations under the noses of his Palestinian Authority captors.

House arrest

In October 2000, under the changed circumstances of the intifada, the PA released hundreds of imprisoned militants - after Israel launched air strikes against its security installations - but Mohammed Deif and one other Hamas leader were reportedly kept in detention "for their own protection."

He was then put under "house arrest" in December 2000 , again for his own protection, and was released once and for all in April 2001.

Since then, he has been a high-profile target for Israel's policy of "targeted killings" or the extra-judicial assassinations of Palestinians blamed for attacks on Israel.

It is thought Mohammed Deif took over as head of Izz al-Din Qassam brigades when Saleh Shehada died when a huge bomb was dropped a house in Gaza killing him and 14 others in July 2002, although Hamas has never said who was promoted to replace Shehada.