In his recent article for The Atlantic, “ The True Origins of ISIS ,” Hassan Hassan makes two related claims concerning the provenance of the Islamic State. One is that analysts have overstated the role of Abu Mus‘ab al-Zarqawi, the Jordanian leader of al-Qaida in Iraq who died in 2006, in crafting the group’s “dark vision”; the other is that the Iraqi religious scholar Abu ‘Ali al-Anbari (né ‘Abd al-Rahman al-Qaduli), who died in 2016, played the greater role in this regard. “It was Anbari, Zarqawi’s No. 2 in his al-Qaeda years, who defined the Islamic State’s radical approach more than any other person,” Hassan writes. “[H]is influence was more systematic, longer lasting, and deeper than that of Zarqawi.” What is more, he contends, “Zarqawi was likely influenced by Anbari, not the other way around.”

I am not convinced of these conclusions, primarily because the basis presented for them—a 96-page biography of Anbari written by his now-deceased son and published in July by Islamic State dissidents—does not bear them out. This biography is an important source for the history of the Islamic State, and Hassan is right to draw our attention to it. It details the hugely important role played by Anbari as a jihadi actor since the early 2000s, and particularly following his release from prison in 2012 when he became one of the Islamic State’s senior leaders. Yet the document says little about Zarqawi, and nothing about Anbari’s influence on him.

In January 2004, when Zarqawi wrote his famous missive to Osama bin Laden outlining a strategy for attacking the Shi‘a in Iraq, it would appear from the document that he had met Anbari once, in Baghdad in 2002.* Hassan writes that Zarqawi’s “idea for targeting the Shiites probably came from native Iraqis like Anbari,” which could be true. But the biography does not tell us this; nor does it suggest that one of these Iraqis was “possibly even Anbari himself.” It does not impute ideological influence to Anbari over Zarqawi at all. It is not clear how close the two were before Anbari became Zarqawi’s deputy in late 2004 (or perhaps slightly thereafter). Apart from their one meeting in 2002—and the fact that Anbari unwittingly produced gun silencers for Zarqawi’s group before the U.S. invasion—what contact they may have had before this time is not discussed. When they did forge a partnership, Zarqawi was the senior partner. Anbari had been second-in-command of an insurgent group in northern Iraq called Ansar al-Sunna. The biography relates that Anbari wanted to join forces with Zarqawi and his group, which had been retitled al-Qaida in Iraq after Zarqawi pledged fealty to Bin Laden in October 2004. Anbari failed to strike a unity agreement, ultimately leaving Ansar al-Sunna to become Zarqawi’s subordinate.

In 2005, according to the biography, Anbari was imprisoned at Abu Ghraib for six months. Upon his release, he went on a mission for Zarqawi to Waziristan to meet with the al-Qaida leadership. Following this, in January 2006, he became head of a consortium of jihadi groups, including al-Qaida in Iraq, called the Mujahidin Shura Council. This leadership is significant as the council would gradually morph into the Islamic State of Iraq, which was declared in October 2006. The biography attributes the idea for the council mainly to Anbari. However, a June 2006 death notice for Zarqawi by al-Qaida in Iraq credits the Jordanian with “the beneficial influence on establishing this council to become the first stone of the Islamic state that will be erected, God willing, in the land of the two rivers.” And an August 2016 issue of the Islamic State’s weekly newsletter asserts that leadership of the council was to be rotational. In any event, neither Zarqawi nor Anbari was present at the creation. The former had been killed in June, the latter arrested in April. Anbari would remain in prison until 2012, his role during this period confined to indoctrinating his fellow inmates.

Significantly, the biography points to a shared ideological link between the two men. Anbari’s ideological formation was complete only after 9/11, when he read the works of Abu Basir al-Tartusi, Sayyid Imam al-Sharif, and Abu Muhammad al-Maqdisi. The last of these was Zarqawi’s teacher and longtime prison companion. It would appear, then, that Zarqawi and Anbari were influenced by the same strain of Jihadi Salafi thought emanating from the pens of a number of radical clerics in the Middle East. But Zarqawi was influenced by it first. Both men would take a more extreme—more violent and sectarian—approach to this ideology than al-Maqdisi himself, and Iraqis were likely critical to shaping it. To be sure, Zarqawi was not acting alone, and many lesser-known jihadis from Iraq, such as Anbari, occupied key positions alongside him. Another was Abu Hamza al-Baghdadi, who served on al-Qaida in Iraq’s Shari‘a Council. I agree that “it is too simplistic to say that ISIS was Zarqawi’s brainchild.” But it is a stretch to infer, from the evidence at hand, that Anbari’s role was the more foundational.

Furthermore, the biography does not challenge the view that it was Zarqawi who introduced the extreme violence that would become the Islamic State’s hallmark. By all accounts, Zarqawi’s influence in this regard was the Egyptian scholar Abu ‘Abdallah al-Muhajir, with whom he affiliated in Afghanistan. As Brian Fishman writes in his book The Master Plan: ISIS, Al-Qaeda, and the Jihadi Strategy for Final Victory, “[I]t was Abu Abdallah who defined Zarqawi—and the Islamic State’s—embrace of sectarianism, brutality, and suicide tactics that have come to define Zarqawism’s adherents.” The first book published by the Islamic State’s printing press in 2014 was Abu ‘Abdallah al-Muhajir’s Issues in the Jurisprudence of Jihad, known commonly—and aptly—as The Jurisprudence of Blood. As Charlie Winter and Abdullah K. Al-Saud have pointed out , the book opens with a quote by Zarqawi acknowledging al-Muhajir’s role in convincing him of the validity of suicide operations.

It is worth recalling here just how celebrated Zarqawi is in the Islamic State, both as a religious thinker and as a dynamic leader. Far from being the semi-literate thug he is sometimes made out to be, Zarqawi spoke impeccable classical Arabic as evidenced by the dozens of hours of recorded speeches and lectures he left behind—nearly 700 pages in transcription . These are frequently quoted by the group. For instance, an Islamic State video filmed in Syria in 2015 shows a man telling the people of Saudi Arabia:

O people of the Land of the Two Holy Sanctuaries, listen to just three lectures by the mujahid shaykh, the heroic leader, “the commander of the martyrdom-seekers,” Abu Mus‘ab al-Zarqawi, may God have mercy on him, who ignited volcanoes in the face of the Rejectionists [i.e., the Shi‘a], who was martyred approximately ten years ago. Listen to these three lectures, titled “Has Word of the Rejectionists Reached You?” They shall bring every devoted Muslim to have as one of his greatest hopes and highest objectives the killing of the Rejectionists in particular among the enemies of God.

His legacy is also commonly invoked by the leaders of the Islamic State. In April 2013, for example, when Abu Bakr al-Baghdadi announced the expansion of the Islamic State of Iraq to Syria, recasting it as the Islamic State of Iraq and al-Sham, he reaffirmed his commitment to the “path” laid down by Zarqawi. “May Shaykh Zarqawi be delighted in his resting place,” he said, “for the path that he tread, whose waymarks he established and guided toward, those who came after him followed it. And we, God willing, are following it as well.” In the absence of further evidence, the path belongs to Zarqawi above all.

* Correction, December 9, 2018: An earlier version of this post stated that Zarqawi‘s letter was written in February 2004, which is the date noted in Zarqawi‘s collected works (p. 58.) In fact, the undated letter was discovered in mid-January 2004, so it cannot have been written later than then. It may also be worth noting Jean-Pierre Milelli‘s speculation (Al Qaeda in Its Own Words, p. 249) that the real author of this letter was Abu Anas al-Shami, Zarqawi‘s principal Shari‘a adviser in Iraq before his death in September 2004. Al-Shami is the author of a book condemning the Shi‘a.