Story highlights Kassig is the fifth Western hostage ISIS apparently beheaded 
 
 He converted to Islam during his captivity and also went by the name Adbul Rahman Kassig 
 
 He was a former U.S. soldier who became a medical worker 
 
 He wanted to help the victims of war and was captured in Syria a year ago 
 
 American aid worker and former soldier Peter Kassig was beheaded by ISIS terrorists, the White House confirmed Sunday, hours after a video claiming to show the victim surfaced online. 
 
 ISIS held Kassig as a hostage and in previous communications had threatened his life. 
 
 The video shows the aftermath of a beheading in which the victim is not clearly recognizable. 
 
 President Barack Obama confirmed the 26-year-old's beheading, saying Kassig "was taken from us in an act of pure evil by a terrorist group that the world rightly associates with inhumanity." 
 
 Kassig, who converted to Islam in captivity, also went by the name Abdul-Rahman Kassig. 
 
 He first traveled to the Middle East as a U.S. soldier and returned as a medical worker, feeling compelled to help victims of war. 
 
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 He did aid work in Syria, where he was captured. He was held hostage for over a year. 
 
 "We are heartbroken to learn that our son, Abdul-Rahman Peter Kassig, has lost his life as a result of his love for the Syrian people and his desire to ease their suffering," Kassig's parents, Ed and Paula, said in a statement. 
 
 The parents released a previously unpublished audio recording of their son, recorded by a journalist before Kassig was taken captive. 
 
 "You know we would have a chance here to make up for a lot wrong that we did in this part of the world if we stepped in, in the right way," Peter Kassig says in the recording. "If we just as a country did what other people helped me to do in that hospital. How much did I impact the political situation inside Syria? None. How much did I impact the political situation back home? None. But what I did do is that over period of time in that hospital I was able to share a little bit of hope and comfort with some people." 
 
 The Kassig family expressed heartbreak over the beheadings of the other Westerners who came before their son, and asked for prayers for the safe return of other captives. 
 
 "While ISIL revels in the slaughter of innocents, including Muslims, and is bent only on sowing death and destruction, Abdul-Rahman was a humanitarian who worked to save the lives of Syrians injured and dispossessed by the Syrian conflict," Obama said. 
 
 ISIL is another term for the group ISIS, the Islamic State in Iraq and Syria, which calls itself simply the Islamic State. 
 
 The video 
 
 A familiar figure appeared in Sunday's beheading video, dressed in all black and speaking with what sounds like an English accent. 
 
 A man fitting the same description appeared in previous videos of the apparent beheadings of other Westerners. 
 
 But this recording is different from previously released ones. It is longer, almost 16 minutes, and does not include a statement by the victim, as previous ones had. 
 
 And it is utterly brutal, showing in graphic detail the beheadings of other men, whom militants claim are pilots for the Syrian government. 
 
 The narration spends much time on ISIS' history and the figure taunts Obama, saying he will have to return troops to Iraq in greater numbers than before. 
 
 And for the first time in such a video, the speaker names the place where he is standing with the victim -- in the town of Dabiq in Aleppo province, Syria. 
 
 The fifth Westerner 
 
 Kassig is the fifth Westerner whom ISIS claims to have beheaded via video messages. 
 
 The first was U.S. journalist James Foley. A video of his killing was posted online in mid-August, just over a week after Obama approved "targeted airstrikes" against ISIS. 
 
 In early September, ISIS released a video showing the beheading of U.S. journalist Steven Sotloff. Sotloff's apparent killer spoke in what sounded like the same British accent as the man who purportedly killed Foley. 
 
 Less than two weeks later, ISIS announced in a video the apparent killing of British aid worker David Haines. 
 
 And on October 3, ISIS released a video showing the apparent beheading of hostage Alan Henning. 
 
 Secretary of State John Kerry praised Kassig's compassion and reiterated the goal of defeating ISIS. 
 
 "This was a young man who traveled to one of the world's most dangerous places to care for the innocent victims of a bloody conflict, and fearlessly dedicated himself to helping those in need," Kerry said. "There can be no greater contrast than that between Abdul-Rahman's generosity of spirit and the pernicious evil of ISIL." 
 
 Plea for mercy 
 
 Kassig's life was threatened on the video that showed Henning's killing. 
 
 A week after its release, Kassig's family released a YouTube video of their own, asking his captors to show mercy and free him. 
 
 Kassig's mother, Paula, addressed her son in the video. "We are so very proud of you and the work you have done to bring humanitarian aid to the Syrian people," she said. 
 
 The couple noted they were releasing the video on the day of Islam's Eid al-Adha, or the Festival of Sacrifice, when Muslims slaughter lambs, goats, sheep and cattle and distribute the meat to the poor and their families. 
 
 A native of Indiana, Peter Kassig founded Special Emergency Response and Assistance, a nongovernmental organization aiding Syrians fleeing the civil war there. 
 
 From 2012, he delivered food and medical supplies within and outside Syria and provided trauma care and training, his family said. 
 
 Soldier, helper, captive 
 
 Kassig's journey began when he joined the U.S. Army Rangers in 2006 and deployed to Iraq in 2007. He was honorably discharged for medical reasons after a brief tour and returned to the United States to study political science and train for 1,500-meter races. But something wasn't right. 
 
 "I was going to school with kids who look the same, were the same age as me, but we weren't the same," he said in an interview with CNN in 2012. "I wanted more of a challenge, a sense of purpose." 
 
 In 2010, Kassig took time off and began his certification as an emergency medical technician. 
 
 In the two years that followed, he fell in love, got married and quickly divorced. Devastated and heartbroken, he went back to school, but he couldn't shake his depression. 
 
 "I needed a game changer," he said. 
 
 He eventually traveled to Lebanon and founded SERA to deliver food and medical supplies to swelling refugee camps. 
 
 On October 1, 2013, he was "detained" on his way to Deir Ezzor in eastern Syria, his family said. 
 
 "Peter really believed that an individual can make a difference in the world through their love and compassion and intelligence," said Margaret Brabant, Kassig's college adviser and a professor at Butler Univeristy in Indianapolis. "... That is the message that I think Peter would want me to convey." 
 
 Hostages tortured before beheadings ||||| Image copyright Kassig Family Image caption Mr Kassig's parents said they were proud of his aid work in Syria. 
 
 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." 
 
 Image copyright Kassig Family 
 
 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 
 
 Abdul-Rahman Kassig's letters home 
 
 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. 
 
 Image copyright Kassig family Image caption With his mother Paula at Cumberland Falls State Resort Park near Corbin, Kentucky, in 2000 
 
 Image copyright Kassig family Image caption Fishing with his father Ed near the Cannelton Dam on the Ohio River in southern Indiana in 2011 
 
 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. 
 
 Image copyright AP Image caption Abdul-Rahman Kassig founded the relief organisation Sera 
 
 Image copyright Kassig family Image caption Helping a wounded man near Deir Ezzor, Syria, in August 2013 
 
 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 
 
 Media playback is unsupported on your device Media caption In the video, Abdul-Rahman Kassig's parents urge his captors to "show mercy" 
 
 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." ||||| Army Ranger veteran Peter Kassig is shown here delivering aid in Lebanon’s Bekaa Valley in May 2013. (Photo courtesy the Kassig family) 
 
 The possible next victim of the Islamic State militant group is Army Ranger veteran Peter E. Kassig, who moved to the Middle East to do humanitarian work before being taken hostage. 
 
 Kassig is shown at the end of a video released Friday that depicts the apparent beheading of Alan Henning, a British humanitarian aid worker who was taken hostage in Syria last year. Kassig started a small medical relief company known as Special Emergency Response and Assistance, or SERA, in 2012 that has headquarters in Gaziantep, Turkey, according to the company’s LinkedIn page. The city is close to the Syrian border and a way station of sorts for relief workers and journalists. 
 
 Kassig also was an employee with TYR Solutions LTD, a British firm that provides security and consulting and training for individuals planning to go to war zones, according to his LinkedIn profile. 
 
 Kassig enlisted as an infantryman, and was in the Army from June 2006 to September 2007 before being medically discharged as a private first class, Army officials aid. He was with the Army’s famous 75th Ranger Regiment from October 2006 to September 2007, and deployed with them to Iraq from April to July 2007. 
 
 Kassig said in an interview published by Time magazine last year that he traveled to the Middle East in 2012 after leaving the Army and while on spring break from Butler University in Indiana. He wanted to learn about the humanitarian crisis in Syria firsthand and see what he could do to raise awareness about it. 
 
 In a web page raising funds for his cause, the former soldier said he felt that more could be done to help the Syrians, and thought the most effective way was “through a close connection to those who were in desperate need, by meeting them where they were.” 
 
 “We may not have much but I have always felt that the reasons why you do something are as important as what you do,” he wrote. “This is about making a difference not just through material goods, but also the exchange of ideas and experiences that the interanational [sic] community benefits from through this type of iniative [sic].” 
 
 In a 2012 interview with CNN, Kassig said that he first traveled to the Lebanese capital of Beirut where he studied how complicated the conflict was. He said some people questioned what he was doing. He told CNN he also wondered whether America was doing enough to help, although he didn’t support military intervention. 
 
 “This is real, and it’s scary stuff, and it’s sad what is happening to people here,” he told CNN. “People back home need to know about it, they need to know. Sometimes you gotta take a stand, you gotta draw a line somewhere.”
– In its latest execution video, ISIS threatened that its next victim would be an American aid worker named Peter Kassig. The 26-year-old is a former Army Ranger from Indiana who served in Iraq in 2007 before being honorably discharged for medical reasons, reports CNN. He enrolled at Butler University upon his return to the US, but traveled to Libya on his spring break to learn about the Syria crisis. "I wanted more of a challenge, more of a purpose," he told the network in a 2012 interview. Eventually, Kassig decided to stay full time to do humanitarian work and founded a relief group called the Special Emergency Response and Assistance, reports the Washington Post. In the last few years, he has been delivering food and medical supplies to refugees from the Syrian conflict. Kassig's parents today released a YouTube video pleading for his release. They refer to their son as "Abdul-Rahman, formerly known as Peter." The Kassigs have previously said that their son converted to Islam while in captivity. A few quotes from Kassig, from CNN and from an interview last year with Time: “This is real, and it’s scary stuff, and it’s sad what is happening to people here. People back home need to know about it, they need to know. Sometimes you gotta take a stand, you gotta draw a line somewhere.” "I am not a doctor. I am not a nurse. But I am a guy who can clean up bandages, help clean up patients, swap out bandages, help run IVs, make people's quality of life a little bit better. This is something for me that has meaning, that has purpose." "In five years, if I can look back on all of this and say that our organization is able to truly help people, that I was able so share a little bit of hope, and that I never stopped learning, then I will know this all stood for something."