BEIRUT, Lebanon — As a little girl, Noor did not know exactly what her father, Hassane Laqees, did for Hezbollah, but even then, she knew she might lose him early. During his long absences, she recalled recently, she would gaze at a photo of him lying asleep and imagine that she was seeing his corpse.

Last month, Mr. Laqees was gunned down in a southern Beirut parking garage by unknown assassins, and Noor, now 28 and an English literature teacher, learned along with the rest of the country who he was: Hezbollah’s master technician and logistics expert, eulogized by its leader, Hassan Nasrallah, as a beloved friend and one of the group’s “bright minds.”

Mr. Laqees joined Hezbollah at its founding in the 1980s as a 19-year-old with a penchant for technology, and he helped build an arsenal more sophisticated than those of many national armies, transforming the Shiite militia into a force that successfully challenged Israel in battle. He helped set up systems of surveillance drones and independent telecommunications, and he used secret bases inside Syria to store the long-range, sophisticated missiles that analysts say are now being funneled into Lebanon.

Israel’s Mossad spy agency put Mr. Laqees on a hit list years ago, identifying him as one of the five men it most wanted dead. From 2008 to 2011, four perished in cloak-and-dagger style. A car bomb in Damascus, Syria’s capital, killed Hezbollah’s military leader, Imad Mughniyeh. A sniper shot a Syrian general on a beach in Tartus. A Hamas official was strangled in a hotel room in Dubai, United Arab Emirates, by assassins who, in an embarrassment for Mossad, were photographed by elevator cameras. And an Iranian general was killed in an explosion at a Tehran missile depot.