But Mr. Streur is not a newcomer to this cause. “I was a lone wolf for a long time,” Mr. Streur said. “A lot of mainstream investors thought this was too radical, too political, too crazy.”

Jim Prescott, a compliance officer at Ariel Investments who has known Mr. Streur for more than 20 years, said he had a theory about where his friend’s passion comes from. “John’s sense of morality, his drive to excel — that comes from somewhere out there in Wisconsin,” Mr. Prescott said.

Mr. Streur grew up in Milwaukee in a family that he said “aspired to be middle class,” but always fell short. He excelled in high school sports and was offered football scholarships by several top colleges, but turned them down to try his hand at rowing instead. He wound up winning a national championship in his freshman year at the University of Wisconsin, and by age 20 had made the United States national rowing team. He said it was there he learned that “background, pedigree and privilege matter not” when compared to hard work and determination.

After graduation, Mr. Streur joined the Wall Street investment giant Lehman Brothers. But the fiercely competitive, profit-hungry finance world was an uncomfortable fit, and he said he was quickly disillusioned by what he called “greedy” banking culture.

In August 1990, Mr. Streur left Wall Street to become a partner in a small money management firm, the Burridge Group, in Chicago. It was here that Mr. Streur was first exposed to the idea of responsible investing when his clients asked if he could divest their money from “unsavory” companies, like those involved in tobacco, gambling or guns. Mr. Streur rose to become the president of Burridge, where he worked on divestment drives for 17 years.

During this time, Mr. Streur became increasingly frustrated by the limited impact of socially responsible investing. He went door-to-door on Wall Street trying to convince some of the titans of investment banking that responsible investing matters and should be woven into their business strategies, but faced repeated rejection, he said. In 2007, he said, his own research showed that fewer than 15 responsible investing companies with more than $1 billion in assets were operating in the United States at the time.

A year later, Lehman Brothers, a goliath of investment banking in America, went bankrupt, triggering the global financial crisis of 2008. This proved to Mr. Streur that “the financial system itself didn’t know what it was doing.” He resigned from Burridge Group, now known as AMG Funds, to devote himself completely to socially responsible investing.