After raising their sons on Long Island, Mr. Weisselberg and his wife moved into a Trump-branded apartment building on Manhattan’s West Side, where they lived rent-free for years. He bought a house in South Florida, not far from Mr. Trump’s resort town of Mar-a-Lago, and traveled aboard Mr. Trump’s jet on the weekends. His eldest son Barry went to work for the company running the Wollman Rink in Central Park and acted as a DJ for Mr. Trump’s Christmas parties, where Allen Weisselberg went wild on the dance floor, according to the people present. In 2004, Mr. Weisselberg appeared on an episode of “The Apprentice,” Mr. Trump’s reality show.

“They’re like Batman and Robin,” said Barry Weisselberg’s ex-wife Jennifer, who aided Mr. Vance’s investigation after a contentious divorce. “It’s a team. They are not the best friends. They don’t spend all of their time together, but the world has become so insular to Allen that he doesn’t know anything else.

Mr. Weisselberg had become so ingrained in the fabric of the Trump organization that when Mr. Trump moved into the White House in 2017, he told Mr. Weisselberg, as well as the former president’s adult sons, the management of his company. His income reflected his importance: between 2007 and 2017, his total salary averaged nearly $ 800,000 per year; in 2018, he earned more than $ 977,000 in salary and deferred compensation, according to income tax data obtained by The New York Times in a survey released last year.

Mr. Weisselberg’s attorney, Mary E. Mulligan, declined to comment. A lawyer for the Trump Organization could not immediately be reached for comment.

Even before the indictment, Mr. Weisselberg had in recent years been publicly drawn into Mr. Trump’s controversies and scandals, including investigations into the misuse of charitable funds by the Donald J. Trump Foundation and payments to women on behalf of Mr. Trump to buy their silence on affairs they said they had with Mr. Trump.

Former Trump attorney Michael D. Cohen told Congress that Mr. Weisselberg helped orchestrate a cover-up to reimburse him for a $ 130,000 payment to adult film actress Stormy Daniels, and that together they had concocted false valuations of the company’s real estate holdings to meet Mr. Trump’s needs at all times.