Dude he was fighting the Kurds in Manbij and Efrin with Al-Nusra in like 2016. He founded Al-Nusra, an offshoot of Al-Quaeda, in 2012.
https://www.understandingwar.org/report/jabhat-al-nusra-syria
In January 2012, a group called Jabhat al-Nusra announced itself as al-Qaeda’s Syrian franchise, and the following month al-Qaeda chief Ayman al-Zawahiri called for Sunnis from around the region to join a jihad against the regime. Jabhat al-Nusra gained Syrian and foreign recruits as it scored greater battlefield successes than rival opposition groups.
In April 2013, a separate group formed from the remnants of al-Qaeda in Iraq that called itself the Islamic State of Iraq emerged and exceeded even Jabhat al-Nusra in its brutality
https://www.cfr.org/article/syrias-civil-war
https://en.wikipedia.org/wiki/Battle_of_Ras_al-Ayn_(2012–13)
Overall probably the Kurds.