BEIRUT, Lebanon — He was a Syrian rebel commander who led homegrown fighters like himself and had a prescient view of the conflict: a Syrian insurgency with nowhere else to turn, he said nearly a year ago, would tilt toward foreign fighters and Al Qaeda.

By the time a government airstrike caught him in northern Syria last week, even some of his most fervent admirers believed he had become, in some ways, part of that tilt.

The commander, Abdulkader al-Saleh, 33, was a recognized and accessible leader in a fragmented insurgency that has few. He managed to gather ragtag local militias into the Tawhid Brigades, for a time one of the most organized and effective rebel battle groups, and to bridge the gap between relatively secular army defectors and Islamist fighters.

But when he died Thursday of wounds from an airstrike in Aleppo, he and Tawhid were months into a slow decline from the peak of their influence. The extremist Islamic State in Iraq and Syria had edged out Tawhid as the pace-setting group policing the northern province. And as that group’s foreign fighters stepped up kidnappings, public executions and attacks on Tawhid and its rebel allies, Mr. Saleh disappointed some of his comrades by remaining largely silent, trying to mediate the disputes rather than fighting to prevent the atrocities and infighting that have gutted the revolt from within.