Jeremy Lin may have never won a ring for the New York Knicks. And his star turn at Madison Square Garden lasted mere months. But in that stretch, his electric play propelled a moribund team into the playoffs, rejuvenated bored fans and started a craze: “Linsanity.”

On Saturday, Linsanity came to an end. The journeyman, who spent 15 years on N.B.A. teams and in leagues in Asia, announced his retirement from professional basketball on his Instagram account.

The unlikely star, a walk-on at Harvard who went undrafted, outshined the league’s biggest names in 2012. Few had heard of Lin, a bench player who joined the N.B.A. in 2010, when the Knicks picked him up a year later. And even fewer expected him to stand out.

But by February 2012, Lin was squarely in the spotlight.

That year’s season started the way it often had for the Knicks. Fans were demanding that Mike D’Antoni, the coach, resign; the offense was a mess; and the Knicks appeared destined for another losing season. That’s when D’Antoni decided to give Lin a chance.

The improbable starter led the team on a seven-game winning streak and averaged 22 points a game before the All-Star break. Madison Square Garden was alive again, brimming with the usual fans, like Spike Lee, and the casual fans, many of whom had lost faith in the perpetual losers.

Scalpers got in on the action as demand for tickets soared, with seats in the upper level going for $150, The New York Times reported. Fans wore masks with Lin’s face, while holding up signs that said “Madison Square Guard-Lin.”