ISTANBUL — Suphi Nejat Agirnasli lived a scholar’s life on an island in the Sea of Marmara, a short ferry ride from the center of Istanbul. He was translating a multivolume encyclopedia of psychology from German into Turkish. He often worked in the living room, in sweatpants, looking out at the water.

“He told me that he didn’t want to grow up. He didn’t want to go to the adult world,” said his close friend Omer, a student who asked to be identified by only his first name.

But in August, Agirnasli cleaned out his room and vanished, leaving no indication of his destination. Two weeks ago, the news came that the 30-year-old died after joining Kurdish forces defending the besieged Syrian town of Kobane from Islamic State in Iraq and the Levant (ISIL).

Images from that brief final chapter of his life contrast with earlier photographs of the scholar hunched over his papers. In a portrait taken during his weeks with the Kurdish militia, Agirnasli stands straight, looking directly into the camera, a smile on his unshaven face. He is dressed in fatigues. In a video posted online, he states his name, birthdate and parents’ names. He holds a gun. Explosions can be heard in the background.

In the widening crisis emanating from Syria, Agirnasli’s profile stands out among the hundreds of men and women from Turkey — most of them ethnic Kurds — fighting in Kobane and the other parts of Syria.

Most of the estimated 15,000 volunteer foreign fighters who have been flooding into that theater of war are joining ISIL and other armed groups. But Agirnasli was fighting against them, making him one of the few non-Kurds, perhaps a few dozen men and women, who have taken up arms against ISIL.

“I think it will remain a small phenomenon in terms of fighters who are going across, but you’re seeing the fault lines played out inside Turkey coming from the Syrian conflict,” said Aaron Stein, a Geneva-based associate fellow with the defense think tank Royal United Services Institute. “It’s the militant left who are going to fight for the communist revolution and see the PYD as on the front lines against Islamism.” The PYD, or Democratic Union Party, is a Syrian Kurdish political party whose armed wing has been leading the battle against ISIL in Kobane.

The Turkish far left regards Syria’s three Kurdish autonomous zones as a challenge to President Recep Tayyip Erdogan’s government at home. Those who have joined the Kurds’ fight in northern Syria have come mainly from two separate factions: the Marxist-Leninist MLKP, of which Agirnasli was a member, and the Revolutionary People’s Liberation Party/Front (DHKP/C), which has been designated by the United States as a “terror group” seeking the overthrow of the Turkish state. It has waged an armed struggle inside Turkey for decades, and in 2013 carried out a suicide bombing at the U.S. embassy in Ankara.

The three-year-old war shaking Syria — with more than 200,000 killed — can feel distant from vibrant, cosmopolitan Istanbul. For many, Agirnasli’s death punctured that sense of distance.

His death was marked at a demonstration Sunday on Istanbul’s Asian side, where hundreds of marchers carried red flags past rows of riot police. They unfurled an enormous banner printed with Agirnasli’s portrait — the one depicting the steadfast warrior. They also flew the yellow flag of the People’s Protection Units (YPG), the Kurdish militia with which he fought. The march ended solemnly at the ferry terminal, the flags still flying, the marchers raising victory signs.

A graduate of Istanbul’s elite Bogazici University, Agirnasli was born into a prominent Turkish dissident family. He was raised in Germany, where his parents lived in exile in the deadly aftermath of Turkey’s 1980 military coup. His lineage is steeped in the left-wing struggle with the Turkish state. His grandfather, Niyazi Ağırnaslı, had been a senator for the Workers Party of Turkey and an attorney for three Marxist student activists who were hanged in 1972 following the 1971 military coup.

A dual Turkish-German citizen, Suphi Nejat Agirnasli chose to return to Turkey as a student, enrolling first at Marmara University, then transferring to Bogazici University, where he completed his bachelor’s and master’s in sociology. His friends describe him an intellectual with a deep knowledge of Marxist and post-structuralist theory, and an ordinary guy who loved parties, women, and was prone to bouts of goofy dancing.

And though he was ensconced in the ivory tower of academia, Agirnasli also thought of himself as a revolutionary, in the family tradition. He organized lectures and protests to raise the profile of a series of workers’ deaths in shipyards on the outskirts of Istanbul, eventually writing his master’s thesis on the same topic. “He studied sociology, but never for the sake of academia,” his university friend Omer said. “He studied sociology for his ideas, to learn about revolutionary ideas.”

In 2006, he joined a group of students who traveled to Diyarbakir, a center of Kurdish life and politics, in a show of solidarity during an intense Kurdish protest against the government. He was arrested in 2011 during a police operation against pro-Kurdish activists and academics. “I’m a socialist, and I’m known for this identity. I’m sensitive to the Kurdish issue, but this is not the point,” he told an independent news site following his release. “Socialists and liberals who engage intellectually or politically with the Kurds are subject to a witch hunt in Turkey.”

The few traces he left indicated that his choice to fight and die in Syria was as much personal as it was political. This summer he had complained about his work and lamented the apparent stagnation of Turkish politics — but if he was planning to leave, he told neither his close friends nor his roommates. He had mentioned vague plans to travel to Latin America. For a year he had studied Spanish through an online course. In August, he returned to Diyarbakir, saying the trip was to visit friends. Shortly after, he stopped answering his phone. On the back of his apartment door hung a cloth banner reading,

“ELYUL IS COMING.” Elyul is the Turkish name for September. “We were thinking he went to Costa Rica or Panama,” Omer said.

“Above all else, I made this choice for myself. I haven’t set out for some lofty belief,” Agirnasli wrote in what is thought to be his last letter. “All I wanted to do is bring some spark to the lives of unlofty people, to a world without a spark, to a world which has been reified.”

“He wanted things to be different, but if they weren’t going to be, he didn’t want to be there. I don’t think he saw things in this country changing for the better,” said Jamie Lynn Buehner, an American English teacher and poet who shared the island apartment with Agirnasli.

In a concrete courtyard at the university last week, students gathered to remember Agirasli, and to collect donations for an aid convoy headed the next day to the border with Kobane. Olcay Celik, a doctoral candidate in philosophy at Bogazici who knew Agirnasli through activist groups, was spray-painting a large black banner. “I believe that every one of us now feels ashamed,” he said. “So we are ashamed of not being like him.”

His father, Hikmet Cur, is not ashamed. In a statement quoted in Turkish media, he said of his son, “He chose revolutionary solidarity while he had other, bright lives ahead. He kept his word. He did not disappoint me.”