Imad Mughniyeh, killed by a car bomb in Damascus on Tuesday night, was a top military leader of the Lebanese Hizbullah organisation, which is mourning him today as a "martyred" hero of its 20-year campaign against Israel and the US.
Mughniyeh has been on the FBI's most wanted list since the 1980s, long before al-Qaida and Osama bin Laden became bywords for terrorism. Working with a shadowy Shia group known as Islamic Jihad, he was blamed for the kidnapping of western hostages in Beirut – including the Briton Terry Waite – and a 1983 bombing that killed 240 US marines in the Lebanese capital.
In 1984, Mughniyeh was said to have been behind the kidnapping and killing of the CIA station chief in Beirut, William Buckley. From the start he was linked closely to Iran's Revolutionary Guards, still Hizbullah's strategic partner. He spent much of the 1990s in Tehran. He was indicted in the US for the 1985 hijacking to Beirut of a TWA airliner in which a US navy diver was killed.
Western intelligence agencies have described Mughniyeh as head of the jihad council within Hizbullah's ruling shura council.
Israel saw him as the terrorist "mastermind" behind the planning for Hizbullah's July 2006 war with the Jewish state, which began with the audacious cross-border kidnapping of Israeli soldiers the organisation hoped to swap for Lebanese prisoners.
It was no surprise that Hizbullah blamed Israel's Mossad secret service for the killing, nor that the Syrian government, doubtless embarrassed by the attack in the heart of Damascus, remained silent.
If Israel was behind the assassination – and it has strongly rejected any involvement - it will be seen as a deliberate signal that it could target leaders of the Palestinian Islamist movement Hamas, which has offices in the Syrian capital.
Another possibility is that the bombing was the work of agents linked to the pro-western Beirut government, which is at odds with the Shia organisation and its Syrian backers. The CIA has been pursuing Mughniyeh for years.
The killing electrified Beirut, already tense on the eve of Thursday's mass rally commemorating Rafiq al-Hariri, the former Lebanese prime minister, whose assassination three years ago was widely blamed on Syria.
Israeli leaders were furious last month when Hizbullah's leader, Sheikh Hassan Nasrallah, made the macabre boast that the group was holding the body parts of several Israeli soldiers. Nasrallah has always claimed that Hizbullah won the 2006 war, taunting the Israelis at every opportunity.
"Israel had an account to settle with Mughniyeh," Eyal Zisser, an Israeli academic expert, told al-Jazeera TV. But he noted that the Lebanese fugitive was wanted by 42 other countries. Israel killed Nasrallah's predecessor, Abbas Musawi, in 1992.
Mughniyeh, aged around 46 and reportedly known to his followers as Haj Radwan, was rumoured to have had plastic surgery and to have been living underground in Beirut's southern suburbs, Hizbullah's stronghold.
Mughniyeh's brother was killed in a similar attack in Beirut in 1994, though reports at the time suggested Imad was the real target.
In this murky area hard facts are more difficult to come by than speculation and misinformation, but some reports have suggested Mughniyeh was in charge of Hizbullah's operations abroad, including attacks on Israeli and Jewish targets in Latin America in the 1990s.