The US strike on Baghdad's international airport early Friday also killed the PMU leader's personal friend and top commander in Iran's Revolutionary Guard Corps, Qasem Soleimani.
Iraqi paramilitary shot-caller Abu Mahdi al Muhandis, killed early Friday in a US strike on Baghdad, was seen as Tehran's man in Iraq and a sworn enemy of the US.
The US strike on Baghdad's international airport early Friday also killed his personal friend Qasem Soleimani, a top commander in Iran's Revolutionary Guard Corps (IRGC).
The men both died in a strike on a convoy belonging to Personal Mobilisation Units (PMU) or Hashd al Shaabi, an Iraqi paramilitary force with close ties to Iran, whose deputy chief was Muhandis.
It came just days after Hashd supporters attacked the American embassy in Baghdad, provoking anger in Washington.
Muhandis –– the widely-used nom-de-guerre for Jamal Jaafar al-Ibrahimi –– was among the pro-Iran mob laying siege to the embassy on Tuesday.
In addition to holding the deputy commander position in the Hashd al Shaabi, Muhandis was also the founder of the Kataib Hezbollah or Hezbollah Brigades.
Known for his virulent anti-Americanism during the US-led occupation in Iraq, Muhandis also built up close ties to Iran over decades.
"Muhandis was demonstrative of how Iran built its network of proxies in Iraq," said Phillip Smyth, a US-based researcher focused on Shia armed groups.
"He has a history with basically every major network Iran had in Iraq. You would not have found a stronger ideal" of Iran's influence in the country, he said.
Muhandis, the early years
Born in 1953 in Iraq's southern Basra, Muhandis held both Iraqi and Iranian citizenship.
He began his political life with the Dawa party, a Shia group that was crushed by Iraqi dictator Saddam Hussein in the 1970s.
Like others in the party, including the future prime minister Nouri al Maliki, Muhandis fled abroad and joined forces with Iran. He spent time in Kuwait as well where he was sentenced to death in Kuwait for involvement in the 1983 bomb attacks on US and French embassies there but fled the country.
In the 1980s, during the Iran-Iraq war, he was a leading commander in the Badr Corps, a unit of Iraqi fighters founded in Iran in opposition to Saddam.
After Saddam's ouster in the US-led invasion in 2003, Muhandis returned to Iraq and briefly served as a member of parliament in Iraq following the 2005 elections.
In 2009, the US sanctioned both Muhandis and Kataib Hezbollah as "terrorist" entities.
Washington said he ran "weapons smuggling networks and participated in bombings of Western embassies and attempted assassinations in the region."
Michael Knights, an expert at the Washington Institute, described Muhandis as "the most inveterate opponent of the United States" among Iraq's Shia armed groups.
His Hashd legacy
He was later appointed deputy head of the Hashd, founded as a loose network of Shia-majority factions fighting the Daesh in Iraq.
It was later absorbed into Iraq's formal security forces, but some of its more hardline factions, including Kataib Hezbollah, still operate independently of Baghdad.
"Muhandis worked assiduously to develop the Hashd into an organisation that was neither subject to full prime ministerial command nor subordinate to the conventional security forces," said Knights.
Although he worked under Faleh al Fayyadh, also Iraq's national security adviser, Muhandis was widely recognised as the Hashd's "real" leader, observers said.
He had both the utmost loyalty of its forces on the ground and control over its financial resources.
That made him "the central nervous system" of the IRGC's Quds Force in Iraq, Knights wrote last year.
He was a personal advisor to Quds head Soleimani, with the two pictured on multiple occasions in warm embraces.
Like the Iranian commander, Muhandis sported a white beard and kept his white hair swept into a neat coif.
He wore glasses and spoke fluent Persian.
Despite his high-profile position within the Hashd, Muhandis rarely appeared in public or delved into politics.
He broke his usual silence last year to blame the US and Israel for a string of mysterious blasts on Hashd bases.
It remains unclear who could replace him, Smyth said, as it would be challenging to find someone with such a close ideological and personal relationship to Iran.