Abu Musab al-Zarqawi
Abu Musab al-Zarqawi was the leader of ISIS's predecessor organization, Al Qaeda in Iraq. Al Qaeda in Iraq split from the central Al Qaeda terrorist organization in 2004. As leader of Al Qaeda in Iraq, Zarqawi emphasized sectarian warfare, condoned attacks on Shia Muslims and introduced beheading videos as a common propaganda feature. Letters between Zarqawi and Al Qaeda leadership revealed plans for the territorial expansion of his group in Iraq, which ISIS would use as a foundation for its own caliphate later on, after Zarqawi's death in 2006. Though Zarqawi didn't found ISIS, which officially formed after his death, most scholars consider him to be the originator of ISIS, including ISIS itself which named its childhood education programs after him.