“I built what I built myself.”

This boast has long been at the core of the mythology of Donald Trump, Self-Made Billionaire. As the oft-told story goes, young Mr. Trump accepted a modest $1 million loan from his father, Fred, a moderately successful real estate developer from Queens, and — through smarts, hard work and sheer force of will — parlayed that loan into a multibillion-dollar global empire.

It’s a classic American tale of ambition and self-determination. Not Horatio Alger, exactly, but appealing, and impressive, nonetheless.

Except that, like so much of what Mr. Trump has been selling the American public in recent years, this origin story was a sham — a version of reality so elaborately embellished that it qualifies as fan fiction more than biography. Also, as we’ve come to expect from Mr. Trump, the creation of this myth involved a big dose of ethically sketchy, possibly even illegal activity.

As an in-depth investigation by The Times has revealed, Mr. Trump is only self-made if you don’t count the massive financial rewards he received from his father’s business beginning as a toddler. (By age 3, little Donald was reportedly pulling in an annual income of what today would be $200,000 a year.) These benefits included not only the usual perks of hailing from a rich, well-connected family — the connections, the access to credit, the built-in safety net. For the Trumps, it also involved direct cash gifts and tens of millions in “loans” that never charged interest or had to be repaid. Fred Trump even purchased several properties and business ventures, putting ownership either fully or partly in the names of his children, who reaped the profits.