US journalist James Foley is the first known western person to be murdered by Islamic State militants - but similar brutal methods of execution have been used on hundreds of people in Iraq.
The group's leader, Abu Bakr al-Baghdadi, was already on America's 'most wanted' list - and some have called him the next Osama Bin Laden.
ITV News diplomatic correspondent John Ray reports on the extremist leader, and the ruthless army he commands.
Warning: The following video contains some distressing images
A British family have told ITV News of their devastation after discovering a close relative is fighting with the Islamic State in Iraq.
A French journalist who was held hostage with James Foley in Syria has told ITV News it was "devastating" to see his murder.