Hamas's top military commander Mohammed Deif, whose wife and son were killed in an air strike in Gaza, is Israel's most wanted man who has defied assassination attempts for years.
In the war between Israel and Hamas, Deif has been a shadowy if hardline presence, refusing to countenance a truce until Israel ends its eight-year blockade of the Palestinian enclave.
Born in the Khan Yunis refugee camp in southern Gaza in 1965, Deif has been involved in Hamas's operations for more than 20 years, plotting suicide bombings inside Israel, kidnapping soldiers, firing rockets and helping plan the tunnels used to launch attacks.
He was appointed head of Hamas's military wing, the Ezzedine al-Qassam Brigades, in 2002 after the death of his predecessor, Salah Shehade, in a raid.
It was the ultimate promotion and the climax of a two-decade career in militancy.
His involvement with the Islamist movement in Gaza began in the 1980s when, as a biology student close to the Muslim Brotherhood, he headed the Islamists' union at Gaza Islamic University.
With the eruption of the second Palestinian Intifada in 2000, Deif escaped, or was freed, from a prison run by Yasser Arafat's Palestinian Authority.
His escape -- or liberation, as it is unclear whether he was freed or not -- angered the Israelis, who had had him in their sights for more than a decade by then.
Shortly after he was named Hamas's military head, Israel launched its fifth bid to assassinate him in Gaza.
That attack left him severely wounded, and some rumours suggested he had been left paraplegic, although these were never confirmed, largely due to the secrecy surrounding the details of his life.
Deif delegated the leadership of the brigades to his deputy, Ahmed Jaabari, thus earning the nickname the "cat with nine lives" among his enemies, and cementing his reputation inside Gaza.
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- Master of disguise -
Only a few, poor-quality photographs of Deif are known to exist, the most recent taken some 20 years ago.
His hiding place is unknown, and he is reported to be a master of disguise who is able to blend seamlessly into the population.
The mysterious commander uses no technology that might allow the Israelis to track him, a Hamas official told AFP on condition of anonymity.
He may have learned caution from the death of his mentor, Yahya Ayash, killed in 1996 by a mobile telephone booby-trapped with explosives by Israeli secret services.
Deif's real name is Mohammed Diab al-Masri, and he owes his 'nom de guerre', which is Arabic for guest, to his habit of constantly changing his location, the Hamas official said.
He described Deif as a man who is "polite, discreet, softly spoken" and fascinated by "military strategy".
The elusive leader's public statements are extremely rare. In 2012, he warned Israel against launching operation "Pillar of Defence", which was aimed at halting rockets fired by militants in the Gaza Strip.
After the death of his mentor Ayash, who passed on his explosive-making expertise, he took on the role of "engineer for the Ezzedine al-Qassam brigades", the Israeli army says in its blog.
The Israelis see him as "the brains" behind the campaign of suicide bombings that targeted buses and public places in Tel Aviv and Jerusalem until 2006 and consider him "personally responsible for the deaths of dozens of civilians".
"Mohamed Deif deserves to die just like (Osama) bin Laden. He is an arch murderer and as long as we have an opportunity we will try to kill him," Interior Minister Gideon Saar told army radio Wednesday.
He also played a key role in the strategic development of Hamas, the Israelis say.
They claim that Deif was among the militants "who designed the Qassam rockets" -- the Islamist movement's signature weapon that had a range of eight kilometres (five miles) until Iran supplied them with more advanced weapons.