Some of his classmates were cruel, calling him racist slurs and making jokes about his eyes. Having skipped kindergarten, he trailed his classmates in size. His voice changed later than theirs did.

The experience, he said, gave him an affinity for the underdog, and left lasting wounds.

“I’ve never forgotten what it felt like to be young,” he wrote in his 2018 book, “The War on Normal People.” “To be gnawed at by doubts and fears so deep that they inflict physical pain, a sense of nausea deep in your stomach. To feel like an alien, to be ignored or ridiculed.”

Today, Mr. Yang often comes across to voters as exuberant. But he describes himself as “naturally introverted,” and in person, that energy comes across as a switch that can flip on and off. Out of the spotlight he can seem low-key, even occasionally withdrawn.

Mr. Yang thrived academically, and halfway through high school he transferred to Phillips Exeter Academy, a selective boarding school in New Hampshire, the first in a succession of elite institutions that would lead him down the path to corporate law: Brown University, Columbia Law School and a junior position at Davis Polk & Wardwell, the elite New York law firm that he quit after five months.

The work was grueling — and when his officemate, Jonathan Philips, broached the idea of a start-up, Mr. Yang was intrigued, Mr. Philips recalled.

“It’s like he all of a sudden woke up,” Mr. Philips, now a North Carolina-based investor, said, recalling long conversations about “the intersection of economic and social betterment.”

They co-founded Stargiving, a company designed to help celebrities fund-raise for charities. There, Mr. Yang pitched and hobnobbed with powerful people and practiced dealing with the news media.