'Jihadi John', as he was known, has been revealed to be Mohammed Emwazi, a Kuwaiti-born British man, in his mid-20s and from west London.
As a child he attended St Mary Magdalene Church of England Primary School in the Maida Vale area of the capital.
A class mate, who asked not to be named, told the Daily Mirror: "It was a Church of England school and he was the only Muslim in our class. One time we had an RE lesson and he got up and talked about his religion.
"He wrote Arabic on the board to show us what it looked like and how it went in the other direction. He showed us a religious text and spoke about what his religion was about.
"That was when we were eight or nine. He mentioned fasting. His English wasn't very good throughout primary school. He could only say a few words at first - like his name and where he was from.
"He played football every lunchtime and at the after-school football club. Through football, he learned different words and expressions. Like all the guys, he always wanted to be the striker.
"He wasn't so good in school, he was the bottom half of the class, but he was one of the sporty guys. He was popular."
Emwazi has appeared in several IS videos showing the beheading of a number of US and UK hostages.
He is also thought to be the killer of Christian Japanese journalist Kenji Goto.
At the time the killer was the only Muslim in his class but a recent Ofsted report for the school said: "Most pupils are from a wide range of minority ethnic backgrounds and the majority speak English as an additional language."