Mohammed Diab Ibrahim al-Masri, widely known by his nom de guerre Mohammed Deif, was a prominent Palestinian militant leader born on August 12, 1965, in Khan Yunis in the Gaza Strip. He grew up in a refugee family displaced during the 1948 Arab-Israeli War, and his early life was shaped by the socio-political tensions in the region. Deif joined the Hamas movement in the late 1980s during the First Intifada, initially engaging in recruitment and operational activities. He studied civil engineering at the Islamic University of Gaza, where he reportedly earned a degree, and his technical background later influenced his role in developing Hamas's military capabilities, including rocket manufacturing and tunnel construction. Deif quickly rose through the ranks of the Izz ad-Din al-Qassam Brigades, Hamas's military wing, becoming a key figure in planning attacks against Israeli targets. He was accused by Israel of orchestrating numerous suicide bombings and rocket attacks throughout the 1990s and 2000s, including the 1996 Jaffa Road bus bombings and the 2002 Passover massacre, though he evaded capture for decades due to his secretive lifestyle and multiple injuries from assassination attempts that left him partially paralyzed.

In 2002, following the assassination of his predecessor Salah Shehadeh in an Israeli airstrike, Deif assumed command of the Qassam Brigades, a position he held until his death. Under his leadership, the Brigades expanded its arsenal and tactics, focusing on asymmetric warfare such as improvised explosive devices, kidnappings, and cross-border raids. Deif was designated a terrorist by Israel, the United States, and the European Union, with a $5 million bounty on his head from the U.S. State Department. He was criticized internationally for his role in escalating violence, including the abduction and killing of Israeli soldiers and civilians, and was implicated in the 2014 Gaza War's rocket barrages that resulted in civilian casualties on both sides. Despite numerous Israeli operations targeting him—over 12 assassination attempts—he remained elusive, earning the nickname 'the ghost' for his ability to survive, though these incidents reportedly caused severe physical impairments.

Deif played a central role as one of the masterminds behind the October 7, 2023, Hamas-led attacks on Israel, which involved coordinated incursions killing over 1,200 people and taking more than 250 hostages, sparking the ongoing Gaza war. His strategic planning was said to coordinate with Hamas leader Yahya Sinwar, aiming to disrupt Israeli security and draw international attention to Palestinian grievances. On July 13, 2024, Deif was killed in a targeted Israeli airstrike in Khan Yunis, alongside other militants, as confirmed by the Israel Defense Forces; the strike also caused significant civilian casualties, drawing condemnation from human rights groups. He was succeeded by Mohammed Sinwar. Deif's death marked a significant blow to Hamas's command structure, though his legacy remains controversial: hailed by supporters as a resistance icon against occupation, while condemned by critics for promoting terrorism and prolonging conflict.