“I think the bulk of their clientele are people who are a paycheck away from being homeless,” Mr. Warren said in an interview.

As complaints mounted, Mr. Stephens and Mr. Carnes sold part of Integrity Advance to a pawnshop-style loan company, Ezcorp. Eventually the Consumer Financial Protection Bureau accused Integrity Advance of “false and deceptive” tactics, and last year, an administrative law judge recommended to the head of the bureau that the company and Mr. Carnes, its chief executive, pay more than $51 million in fines and restitution to borrowers. Integrity Advance and Mr. Carnes are appealing the ruling.

In its legal action against Integrity Advance, the bureau emphasized Mr. Carnes’s 52 percent ownership of Hayfield, the parent company. Neither regulators nor the news media has ever mentioned Mr. Stephens’s sizable stake. (Mr. Stephens declined to comment.)

If he kept quiet about his role in the embattled payday loan business, he showed no similar reticence in attacking the consumer bureau. In June 2013, he told The Wall Street Journal that the bureau bore some blame for lagging business growth. “The stories we hear about that are pretty scary,” the billionaire said.

During last year’s campaign, Mr. Stephens contributed $3 million to Club for Growth, a conservative political action committee that has pushed Congress to strip the bureau’s enforcement powers.

Along with helping bankroll such Washington battles, Mr. Stephens has recently used his investment bank, Stephens Inc., to start an online video series called “This Is Capitalism” to improve millennials’ opinion of free-market economics.

In his introduction, Mr. Stephens wrote that he hoped the series would counter the notion that the free market is “a system that enriches a few at the expense of the many.”