Buddy Duress, a small-time heroin dealer living on the streets of the Upper West Side who became a sensation in the New York film scene as an actor and muse for the movies “Heaven Knows What” and “Good Time,” which launched the careers of the filmmakers Josh and Benny Safdie, died in November at his home in Astoria, Queens. He was 38.

The death, which was disclosed only in late February, was from cardiac arrest caused by a “drug cocktail” including heroin, his brother, Christopher Stathis, said.

Mr. Stathis said their mother, Jo-Anne Stathis, was seriously ill in November, so he withheld news of the death, hoping to inform her himself at an appropriate time. By early December, he said, he had told her and several other people, but nobody in Mr. Duress’s circle made an announcement. Mr. Duress had been out of the public eye and in jail frequently in recent years.

At the height of his career, in the mid-2010s, directors made trips to Rikers Island to visit and audition Mr. Duress. He acted alongside Michael Cera and Robert Pattinson, and critics said he stole scenes. At the 2017 Cannes Film Festival, he strolled down the red carpet of the Grand Théâtre Lumière, the main theater, to a standing ovation, then shoved his face in front of a French TV camera shouting, “What’s up, Queens?”

He was ungovernable and thrill-seeking, traits that, on the set, gave his performances authenticity but that also led him to squander opportunities. Each time, though, he said he would finally change: He was ready to dedicate himself to acting.