The boys were free to do what they wanted, up to a point. When Billy Graham brought his crusade to downtown Pittsburgh, Ron, a teenager, headed off to the revival on his own. But when he shot a BB gun at a neighbor’s passing car, he lost the gun for good.

His parents did not impose their politics on their sons. But family lore about hyperinflation, property as the safest investment and a great-grandfather’s escape from crushing debt in 19th-century Germany all made an impression. As did a grade-school janitor who hired young Ron to paint the walls and ranted about bankers being “the source of our problems,” as Mr. Paul recalled in one of his books.

Wartime rationing also left a mark. When he saw a local butcher shop ignoring the rules on Saturdays and selling “all the meat you wanted, at a price,” Mr. Paul wrote, it was “my first real-life experience in the free market solving problems generated by government mischief.”

A high school athlete — he wrestled opponents 20 pounds heavier and won the Pennsylvania championship in the 220-yard dash — he was offered a full athletic scholarship to the University of Pittsburgh, even after an injury and crude surgery severely damaged his knee. But he turned down the offer, saying it would be wrong to accept given his doubts that he could compete. In private, he despaired of ever racing again — and railed against a God who, as he told Jerrold, “would give me something and then take it away.”

He went off instead to Gettysburg College, where he paid his way washing dishes and managing a campus coffee shop, the Bullet Hole. His brothers in Lambda Chi Alpha took note of his rectitude. “You’d go out for a beer, and he’d have a Coke,” said James Fuller, a classmate. “He never missed church. He was a very straight shooter.”

“Peer pressure wasn’t going to change him,” said Samuel Blackwell, another classmate. The same went for his politics. Mr. Fuller said he pegged Mr. Paul as “to the right of Attila the Hun.” Others said he was so opinionated that the fraternity’s cook — a local farmer and a liberal Democrat — took delight in goading him into political arguments.

Mr. Paul was pre-med, but he gravitated to economics and political science classes, though he said his college instructors mainly caused him to doubt his own instincts. “They were always trying to beat them out of me,” he said.