Tunisian pastry chef Slim Gasmi died on a Syrian battlefield and was lionized with a hashtag: #martyrdomofabuqatada.

Gasmi, 28, had been trying to build a life for himself and his new fiancee in a working-class Tunis neighborhood, but a radical Islamist roommate persuaded him to travel to Syria to fight in that country’s civil war. By the time he was killed in April more than 1,500 miles from home, he had transformed into a warrior with a long beard and a nom de guerre, Abu Qatada, celebrated on a radical jihadist Twitter feed.

Tunisia, a small North African country of 11 million people, has become the largest source of foreign fighters joining the Islamic State and other extremist groups in Syria and Iraq, according to estimates by the Tunisian government and private analysts. […]