Abdul-Rahman Kassig: Idealist 'simply seeking to help'
Abdul-Rahman Kassig believed it was his duty to alleviate the suffering of people affected by conflict in the Middle East.
Mr Kassig, known as Peter Kassig before he converted to Islam, founded a humanitarian organisation to help refugees who had fled from Syria.
In interviews and letters to his family, Mr Kassig, 26, said he was driven by a "sense of purpose" and a desire to help others after serving with the US military in Iraq.
In 2012, he wrote: "The truth is sometimes I really think I would like to do something else, but at the end of the day this work is really the only thing that I have found that gives my life both meaning and direction."
Abdul-Rahman (aka Peter) Kassig
- Former US Army Ranger
- Served in Iraq in 2007
- Travelled to Lebanon in May 2012, volunteering in hospitals and treating Syrian refugees
- Founded aid organisation Special Emergency Response and Assistance (Sera) in 2012 to provide aid to Syrian refugees
- Captured by Islamic State in October 2013 while travelling to Deir Ezzour in eastern Syria
- Converted to Islam in 2013, changing name from Peter Kassig
A native of Indiana, Mr Kassig "spent his late teens and early 20s searching for his place in the world", his parents Ed and Paula Kassig said in a statement.
He joined the US military and served as an Army Ranger in Iraq in 2007. He was given an honourable discharge from the Army for medical reasons. But on returning home "he felt called to be a peacemaker", according to his parents.
In 2010 he enrolled at Butler University in Indianapolis, where he majored in political science. Mr Kassig described how, in the wake of a brief marriage and divorce, he had needed a "game changer".
He travelled to Lebanon in 2012 during a spring break, volunteering as a medical assistant in border hospitals.
There he helped treat Palestinian refugees and, subsequently, people escaping the conflict in Syria.
During the summer of 2012, he was interviewed by CNN while working at a hospital in Tripoli, Lebanon. He told the crew: "This is what I was put here to do."
He added: "I guess I am just a hopeless romantic, and I am an idealist, and I believe in hopeless causes."
Later that year, he founded a non-governmental organisation named Special Emergency Response and Assistance (Sera), dedicated to providing humanitarian aid for the growing number of people who were fleeing Syria's civil war.
In the summer of 2013, Sera's operational base moved to Gaziantep, Turkey. Mr Kassig located and distributed food and medical supplies to the refugee camps on both sides of the Syrian border. He also provided primary trauma care as well as medical training to civilian casualties in Syria.
According to his family, he "worked closely with and befriended Syrian medical and humanitarian workers who were trying to save lives and restore hope".
The BBC's Paul Wood, who met Mr Kassig while he was on the Turkish-Syrian border, said he "always cut a slightly unworldly figure... open, honest, slightly intense, beguiled by Syria's uprising".
Mr Kassig was working with Sera when he was captured on 1 October 2013 while travelling towards to Deir Ezzor in eastern Syria.
For a year, his parents remained silent at the behest of his captors. Along with his friends inside and outside Syria, his family worked to secure his release.
Excerpt from video appeal by Ed and Paula Kassig
In a statement, his parents said their son's "journey toward Islam" had begun before he was taken captive. In the summer of 2013 he observed the month-long Ramadan fast which had a "great impact" on him.
According to his family, he converted voluntarily while sharing a cell with a devout Muslim, between October and December of the same year. He is said to have taken his faith seriously, praying five times a day and adopting the name Abdul-Rahman.
French hostage Nicholas Henin, who was held with Mr Kassig for four months, described him as "a very dedicated Muslim".
"Peter told me about how important Islam was to him, how much it helped to overcome his situation in captivity," Mr Henin told the BBC.
When the hostages received food, "Abdul-Rahman was basically sharing all of his food but looking for sweets," Mr Henin added. "He was always looking for some extra marmalade."
In a letter to his family received on 2 June, Mr Kassig wrote that he was "pretty scared to die" but said the the hardest part was "not knowing, wondering, hoping, and wondering if I should even hope at all".
He expressed his sadness at the pain his capture had caused those closest to him, adding: "If I do die, I figure that at least you and I can seek refuge and comfort in knowing that I went out as a result of trying to alleviate suffering and helping those in need.
"In terms of my faith, I pray everyday and I am not angry about my situation in that sense."
The letter ends with the words: "I love you."