A founding member of the Islamic State in Iraq and Syria (ISIS), Abu Mohamed al-Adnani was its chief spokesman and propagandist.
He ran an operation that put out slickly produced videos of beheadings and massacres that shocked the world and had recruits rushing to join the group in Syria.
Accounts from arrested ISIS members confirm the 39-year-old Syrian's role as an operational leader as well.
Adnani, whose real name was Taha Sobhi Falaha, oversaw the group's external operations division which was responsible for recruiting operatives around the world and instigating or organising them to carry out attacks.
Intelligence officials in the US and Europe say the unit is a distinct body inside ISIS.
Its command-and-control structure answered to Adnani, who in turn reported only to Abu Bakr al-Baghdadi, the self-proclaimed caliph of ISIS.
Adnani was also being groomed to succeed Baghdadi, analysts say.
Although the unit's main focus has been Europe, external attacks directed by ISIS or those acting in its name have been even more deadly elsewhere.
At least 650 people have been killed in the group's attacks on sites popular with Westerners, including in Turkey, Egypt and Tunisia, according to a New York Times analysis conducted this year.
Even as ISIS has lost much of its territory and operatives, the kind of terrorist attacks abroad that Adnani's division oversees has continued.
In September 2014, Adnani called on Muslims in the West to strike out wherever and however they could. In the year after that speech, at least two dozen plots linked to ISIS were documented.
In some, there were no direct operational ties back to Syria, but there were clear signs that the attacker had, at the least, consumed the terrorist group's propaganda online.
"During the past decade, when it comes to both orchestrating and inciting violence in the West, no other leadership figures in jihadist groups have proven as dedicated or effective as al-Adnani," said Mr Michael Smith II, a terrorism analyst at research firm Kronos Advisory.
NEW YORK TIMES