David Haines had been in Syria for just ten days when he was kidnapped near the Turkish border along with a colleague at French aid agency Acted in March last year. They had been looking for suitable locations for refugee camps.
Last night jihadists from Isis, which calls itself Islamic State, posted a video purportedly showing the murder of the 44-year-old. The video has not been verified by the Foreign Office, but David Cameron has described his killing as an "act of pure evil".
David Haines was born in Holderness, East Yorkshire, and raised in Scotland, where his parents lived in Ayr.
He attended Perth Academy and married his childhood sweetheart Louise, although they later divorced. They have a daughter Bethany, now 17.
Haines worked for the Royal Mail and as an engineer for the RAF. It was while serving in the UN mission in the Balkans that he developed his passion for humanitarian work, and he dedicated the rest of his life to it.
He began working for German charity Arbeiter Samariter Bund (ASB), helping to rebuild post-war Croatia. In 2010 he remarried, settling in Sisak, south of Zagreb, with Croatian wife Dragana. They have a four-year-old daughter, Athea.
Dragana told the Daily Telegraph: "He's everything to us. He's our life. He's a fantastic man and father. Nobody can understand how we are feeling. My daughter keeps asking about him."
In April 2011 he joined Handicap International in Libya, later working in Sudan, where the director of the Nonviolent Peaceforce described him as "very caring".
He later began aid work in Syria, where he was ultimately captured.
Acted, the French agency he worked for, said: "A man's life should never be threatened on account of his humanitarian commitment."
Today prime minister Mr Cameron described David Haines as a "British hero" and praised the "extraordinary courage" of his family.
Mike Haines, David's brother, described him as "like so very many of us, just another bloke".
"David was most alive and enthusiastic in his humanitarian roles. His joy and anticipation for the work he went to do in Syria is for myself and family the most important element of this whole sad affair," he said in a statement released through the Foreign Office.
"He was and is loved by all his family and will be missed terribly."
The full statement from the family of David Haines:
My name is Mike Haines, I am brother to David Haines, who was recently murdered in cold blood.
David was like so very many of us, just another bloke. Born in 1970 to parents who loved us both, our childhood was centred around our family.
Holidays in caravans and tents, days away as a family which we remember fondly.
David and I were brought up to know right from wrong, although we might not with the innocence of youth have always chosen right.
David was a good brother, there when I needed him and absent when I didn't. I hope that he felt the same way about me.
He was, in the right mood, the life and soul of the party and on other times the most stubborn irritating pain in the ass. He would probably say the same about me.
After leaving school he worked with the Royal Mail before joining the RAF as an aircraft engineer.
He married his childhood sweetheart Louise and in the due process of time had a wee lass Bethany.
He was - and no doubt wherever he is - exceptionally proud of Bethany.
David served with the UN in the Balkans, helping people in real need.
There are many accolades from people in that region that David helped.
He helped whoever needed help, regardless of race, creed or religion.
During this time David began to decide that humanitarian work was the field he wanted to work in.
David left the RAF and was employed by Scotrail.
As with every job, David entered into it with enthusiasm.
David met and married his second wife Dragana and they have a four year old daughter Athea.
David was most alive and enthusiastic in his humanitarian roles.
His joy and anticipation for the work he went to do in Syria is for myself and family the most important element of this whole sad affair.
He was and is loved by all his family and will be missed terribly.