WASHINGTON  A senior adviser to Elizabeth Warren, hired to help start the Consumer Financial Protection Bureau, is an investor in and, until recently, served as a director of a company that helps to arrange low-documentation loans for consumers with often-spotty credit histories.

Rajeev V. Date, a former banker who was hired this month as a senior adviser to Ms. Warren, was an active participant in the debate over the Dodd-Frank Act, the financial regulation bill that created the consumer bureau. During that time, he also served as a director of Prosper Marketplace Inc., a so-called peer-to-peer lender that operates an online market to match consumers seeking loans with lenders. In its first four years of operation, more than 25 percent of the loans it helped arrange went into default, according to the company’s financial statements.

Although news reports about the Dodd-Frank debate widely quoted Mr. Date as the leader of a nonpartisan policy institute and a former banking executive, it was rarely reported that Mr. Date (pronounced Dah-Tay) was, at the same time, also being compensated by Prosper Marketplace, which sought to influence the outcome of some parts of the financial regulation law.

The company had hired a prominent lobbyist in Washington during the Dodd-Frank debate, after being penalized by the Securities and Exchange Commission and multiple state securities regulators.