When Mr. Trump’s high school classmates showed up for a Columbus Day parade in New York City, expecting to lead the procession, they were dismayed to find a group of Roman Catholic girls arranged ahead of them. Mr. Trump announced that he would take care of the problem. When he returned a few minutes later, having negotiated a Trump-like deal, the cadets were put at the front of the parade, Mr. Dobias said.

Mr. Trump, he said, “just wanted to be first, in everything, and he wanted people to know he was first.”

St. Martin’s Press provided an advance copy of the book to The New York Times, and Mr. D’Antonio provided excerpts from his interviews with Mr. Trump. (The author interviewed Mr. Trump for more than six hours. The sessions abruptly ended, he wrote, after Mr. Trump learned that Mr. D’Antonio had spoken with a longtime Trump enemy.)

The biography offers candid and sometimes unflattering assessments of Mr. Trump by co-workers, friends, enemies and, most entertainingly, his former wives. “The little boy that still wants attention,” said Marla Maples, his second wife.

“He wants to be noticed,” said Ivana Trump, wife No. 1, who recalled sending him into a fit of rage by skiing past him on a hill in Aspen, Colo. Mr. Trump stopped, took off his skis and walked off the trail. “He could not take it, that I could do something better than he did,” she said.

Asked if she had ever figured out her ex-husband, Ivana Trump said, “Yeah, I figured it out.” But then she added, “Well, I really don’t know.”