Robert Trump, the younger brother of President Trump, said in 2016 that he supported his sibling’s candidacy “one thousand percent.” The brothers were photographed embracing on election night.

But after that, Robert Trump was little heard or seen in public until he put his name on a lawsuit earlier this summer against his niece Mary L. Trump in a futile attempt to stop the publication of her book, which called Donald Trump “the world’s most dangerous man.”

The endorsement of his brother and the prolonged period of silence seemed emblematic of Mr. Trump, who died Aug. 15 at 71 in New York City. The death was announced by the White House. He had been hospitalized for several days after becoming seriously ill.

Robert Trump was the quiet one in comparison with his boisterous brother. He often did what his famous sibling asked him to do, absorbing the criticism that his brother reportedly lobbed at him and remaining loyal until the end of his life.

“It is with heavy heart I share that my wonderful brother, Robert, peacefully passed away tonight,” President Trump said in a statement. “He was not just my brother, he was my best friend. He will be greatly missed, but we will meet again. His memory will live on in my heart forever. Robert, I love you. Rest in peace.”

Robert Stewart Trump was born in New York on Aug. 26, 1948, the youngest of five children of Fred Trump Sr. and his wife, the former Mary Anne MacLeod. The eldest son, Fred Jr., died of an alcoholism-related illness in 1981 at 42.

It was Fred Jr.’s daughter, Mary L. Trump, who this year published a scathing memoir of her time in the family, and her book provides the most vivid account of Robert Trump’s upbringing.

“Donald had discovered early on how easy it was to get under Robert’s pale skin and push him past his limits; it was a game he never tired of playing,” Mary Trump wrote. “Nobody else would have bothered — Robert was so skinny and quiet that there was no sport in tormenting him.”

He graduated from Boston University in 1970 and became an investment banker in real estate finance at Kidder, Peabody and then worked at Shearson Loeb Rhoades.

His life was altered when a tragedy affected his brother’s Atlantic City casino business in 1989.

That year, Steven Hyde, who oversaw Donald Trump’s Taj Mahal casino, was traveling on a helicopter with two other executives when the aircraft crashed in New Jersey, killing all onboard. Donald Trump had overextended himself in building the Taj Mahal casino and had relied heavily on Hyde. With Hyde’s death, Donald Trump asked his brother to oversee operations.

Because of mistakes for which Donald Trump bore at least some responsibility, including overestimating the demand for gambling, Robert Trump had difficulty stabilizing the finances of the Taj Mahal. In a meeting famously described by another former Trump casino executive, John O’Donnell, Donald Trump complained: “We’re going to lose a fortune.”

“Donald, you know there’s just no way to predict these things,” Robert Trump responded, according to O’Donnell’s memoir, “Trumped!”

Donald Trump blew up at his brother, saying: “I’m sure as hell not going to listen to you in this situation. I listened to you and you got me into this,” according to O’Donnell. Robert Trump said, “I’m getting out of here. I don’t need this,” O’Donnell wrote.

O’Donnell said in an interview that the fight between the brothers “changed forever” their relationship. Donald Trump told The Washington Post in a 2016 interview, however, that his brother “never quit” and did a “really good job.”

In 1991, Robert Trump joined his father’s business, Trump Management, where he was reportedly paid $500,000 a year, according to a 2018 New York Times story.

In 1999, when Fred Trump Sr. died, his children faced a decision about how to handle the inheritance. Mary Trump and her brother, Fred Trump III, sought an amount similar to what would have gone to their father, Fred Trump Jr., had he lived. Because one of Fred Trump III’s children had cerebral palsy, he cited the need to pay for his son’s care in seeking his share of the inheritance.

Instead, Robert Trump worked on behalf of Donald Trump and his other siblings to give a much smaller amount to Mary and Fred Trump III. Robert Trump said in an affidavit that the health care for Fred III’s son had been provided “out of the goodness of our hearts,” and he said that Fred Trump III had received $200,000 annually from the Trump family “without lifting a finger.”

Years later, Mary Trump said she learned that the family had given her and her brother a much smaller inheritance in part by concealing how much the estate was worth. That revelation was part of the motivation for her to write her best-selling book about Donald Trump, “Too Much and Never Enough.”

Robert Trump, just as he had in the inheritance lawsuit, acted on behalf of his older brother and other siblings in filing an action seeking to prevent publication of his niece’s book this summer. Robert Trump, who had been out of the public eye since his brother’s election to the White House, issued a statement in which he said he was “deeply disappointed” by Mary Trump’s decision to write the book.

“I and the rest of my entire family are so proud of my wonderful brother, the president, and feel that Mary’s actions are truly a disgrace,” Robert Trump said in the statement. He did not speak publicly about the matter, continuing the near silence he had maintained throughout the presidency. A court allowed the book to be published and let Mary Trump give interviews about it.

Robert Trump’s marriage to the former Blaine Beard, a socialite and philanthropist, ended in divorce. He had adopted her son Christopher from an earlier marriage. At the time of his divorce in 2008, the New York Post estimated Robert Trump’s fortune at $200 million.

In recent years, he lived in Millbrook, N.Y. This year, he married Ann Marie Pallan, according to the New York Post.

In addition to his wife and President Trump, survivors include two sisters, retired federal judge Maryanne Trump Barry and Elizabeth Trump Grau.

Alice Crites contributed to this report.