Peter Kassig, a Muslim convert who adopted the names Abdul Rahman, was honourably discharged from the US military after 15 months, including the three-month stint in Iraq that Isil referred to in yesterday's video.
But he then retrained as a medical emergency technician, studied political science and found his calling helping the people of Lebanon, and later Syria.
Friends and family paint a picture of a devoted humanitarian, who had embraced the values of Islam long before his conversion. After a study trip to Lebanon in 2012, he started volunteering at a hospital in the northern city of Tripoli.
He always wanted to do more, said Ahmed Obeid, a doctor at the hospital. He didn't talk about politics, or religion. He just wanted to help people.
Firas Agha lived with him for six months. They played football, drank coffee, went to the gym. He was just a normal guy, says Mr Agha.
He intended to set up a nimble organisation which would train Syrians to be medical responders, as well as deliver supplies.
He was taking part in a trip to deliver medical aid to Deir ez-Zor on October 1, 2013, when he was kidnapped.