Mohammed Diab Ibrahim al-Masri (Arabic: محمد دياب إبراهيم المصري;‎ 12 August 1965 – 13 July 2024), better known as Mohammed Deif (Arabic: محمد الضيف), was a Palestinian militant and the head of the Izz al-Din al-Qassam Brigades, the military wing of the Palestinian nationalist Sunni Islamist organization Hamas.

Deif was born around 1965 in the Khan Yunis Refugee Camp in the Gaza Strip, to a family that fled or were expelled during the 1948 Palestine war.

[5][6] He reportedly left school temporarily to support his low-income family, later graduating with a bachelor's degree in chemistry from the Islamic University of Gaza in 1988, where he had established a theater group.

He became the head of the al-Qassam Brigades in 2002 and developed the group's capabilities, transforming it from a cluster of amateur cells to organized military units.

In May 2024, the Prosecutor of the International Criminal Court (ICC) applied for arrest warrants for Deif and several other Hamas and Israeli leaders for their war conduct.

[9] Mohammed Diab Ibrahim al-Masri was born on 12 August 1965 in the Khan Younis refugee camp in the southern Gaza Strip.

[12] Although not much is known about the details of his early life and upbringing,[13] he reportedly had to temporarily drop out of school to support his low-income family, working with his father in upholstery and later starting a small poultry farm.

Yahya Ayyash's disciples had ensured the right wing's victory and "derailed the peace process," in the words of the deputy head of the Shin Bet, Yisrael Hasson.

[34] In September 2015, the US Department of State added Deif and three other Hamas leaders to the American list of Specially Designated Global Terrorists.

"[38] Deif has been credited with transforming the al-Qassam Brigades from a cluster of amateur cells to organized military units, described as an 'army,' that are capable of invading Israel.

[21] As the highest-ranking leader of the al-Qassam Brigades, Deif was involved in orchestrating the surprise attack on Israel that commenced the Israel–Hamas war, which, according to a source close to Hamas, he began planning in the lead up to the 2021 Israel–Palestine crisis, motivated by scenes of Israeli forces storming al-Aqsa Mosque during Ramadan.

[39][40] After the attack, a Reuters report stated that over the previous two years, Deif deceived Israel into believing Hamas was not interested in another round of conflict.

[42] On the day of the attack, Deif gave an audio address, his first since 2021, justifying it as a response to the "desecration" of the al-Aqsa Mosque and the killing and wounding of hundreds of Palestinians in 2023.

"[47][b] On 21 November, the court officially indicted Deif for war crimes, stating that he bore responsibility for mass killings, hostage taking and rape during the 7 October attacks.

[50] On 3 September 2024, the United States Department of Justice announced criminal charges against Deif and other Hamas officials for their roles in the 7 October attack on Israel.

[13] As of December 2023, Israeli military and security forces have killed Deif's brother, his nephew, his niece, his wife, his 3-year-old daughter, and his 7-month-old son.

[15] After the 2006 assassination attempt, Deif spent three months in Egypt for treatment of his skull after shrapnel lodged in it, and he continued to take daily tranquillizers to treat headaches.

[17][61] Footage obtained by the Israeli military in December 2023 showed Deif using both hands and walking on his own two feet, though with a slight limp and occasionally with the aid of a wheelchair.

[69][70] The IDF reported that one of Deif's associates and a mastermind of the 7 October attack, the Khan Yunis Brigade commander Rafa Salama, was among the dead.

[78][50] On December 4, 2024, Israeli news channel Kan 11, citing Palestinian sources, reported that Hamas had located Deif's body and buried it in secret.

According to the report, Hamas maintained secrecy over Deif's death due to fears that confirming it would lower the morale of its fighters, and buried him in an undisclosed location due to fears that if Israel discovered the location of his grave, the IDF would dig it up and take his body to use as a bargaining chip in a hostage deal.

[79] On January 30, 2025, the Qassam Brigades, through their spokesperson Abu Ubeida, confirmed that Mohammed Deif, along with six other senior Hamas commanders, died as a result of the Israel–Hamas war.

[21] After acknowledging his death, Hamas began using photos of Deif at ceremonies for the release of the hostages to the custody of the Red Cross as part of the 2025 Gaza war ceasefire agreement.