After 13 years of devastating civil war, Syrian President Bashar al-Assad’s regime was toppled in a stunning offensive led by the rebel group Hayat Tahrir al-Sham (HTS).

The country now confronts an uncertain future—not least of which is how HTS, which evolved out of an al Qaeda affiliate with ties to the founder of the Islamic State, will approach governance.

HTS’s leader, Ahmed al-Sharaa—better known by his nom de guerre Abu Mohammad al-Jolani—has worked for years to distance himself from his al Qaeda roots, but establishing legitimacy in the eyes of the international community, particularly the United States, will be an uphill battle.

There’s also a major question about whether Syria’s instability could cause it to once again become a safe haven for terrorist groups such as the Islamic State to flourish.

Foreign Policy spoke with Aaron Zelin, a terrorism expert and senior fellow at the Washington Institute for Near East Policy who wrote a book on HTS, to find out more about Jolani’s origins, his efforts to rebrand, and what’s potentially in store for Syria now that he’s the country’s de facto ruler.

This interview has been edited for length and clarity.

Click here to read the interview in full.