After a day in the high-flying world of high finance, David M. Solomon knows how to unwind. He can be seen on stage in some of Manhattan’s dance clubs, mixing electronic music as D.J. D-Sol for throngs of partygoers.

For a more tranquil evening, Mr. Solomon enjoys fine food and fine wine, and is known to arrive at steakhouses with a rare vintage from his cellar. For years, Mr. Solomon, a co-president at Goldman Sachs, tasked his personal assistant with helping manage a world-class collection of wine.

But his assistant, Nicolas De-Meyer, was doing much more than simply stocking his boss’s wine cellar in the Hamptons, federal authorities said. Mr. De-Meyer stole some of the most coveted French vintages — worth more than $1.2 million — in Mr. Solomon’s collection and sold them, according to an indictment unsealed on Wednesday in United States District Court for the Southern District of New York.