They fetch his takeout meals and draw him into conversation. They buy him warm coats and scarves and sneakers. Some trade emails about his health, which has been remarkably robust despite an occasional scare. (“He didn’t get to the corner until 5:30 instead of his usual 3,” a neighbor messaged to another on a morning in 2014. “He said he has to down cough syrup twice in the night now, and this time it knocked him out.”)

A physician in the White House arranged for a free chest X-ray. The superintendent at another building lets Mr. Singh into the basement for bathroom breaks. Customers stand guard over his papers until he returns.

A man of quiet ways, Mr. Singh can be gloomy and taciturn one day, lively and opinionated the next; his mood varies with the weather and the headlines. Yet his regulars, most of them middle-aged or older, speak of him with warmth, and something more.

“I’ve stayed with Singh out of loyalty,” said Ken Coughlin, who runs a legal-information website and has been buying The New York Times from him every day for at least 20 years, at a cost now of about $1,250 a year. “He’s a fixture in the neighborhood, a fixture in my life. I want to support him.”

Lee Herman, a curator emeritus at the American Museum of Natural History, has been a patron since Mr. Singh first showed up. "You see this guy, with wind chill of 11 below, out there selling papers,” Mr. Herman said. “He’s got a life that’s extraordinary — what he has to go through to live.”

These neighbors know little about that life, or one another’s, but Mr. Singh knows all their preferences and quirks. He notices when they miss a day, and offers to save their papers. He serves noncustomers, too — clearing trash from the sidewalk, warning subway riders when trains aren’t running, feeding the birds and dogs (“my other customers,” he calls them), holding the door when White House residents need a hand.