Hillary Rodham Clinton’s recruitment of Gary Gensler, a former top federal Wall Street regulator, as her campaign’s chief financial officer was meant to show donors she is serious about avoiding the overspending that plagued her 2008 presidential campaign, according to people briefed on the matter.

It was also the latest indication that Mrs. Clinton is prepared to take a tougher stance toward the financial industry. Mr. Gensler, as chairman of the Commodity Futures Trading Commission from 2009 to 2014, overhauled the commission from one of Wall Street’s most lax regulators to one of its most aggressive, and campaigned to rein in risk-taking in response to the financial crisis.

But Mr. Gensler is also someone whose email practices, as the head of a federal agency, were the subject of sharp criticism — much as Mrs. Clinton’s email use as secretary of state has been.

A campaign spokesman declined to comment Friday on Mr. Gensler’s hiring, which was first reported Thursday by Bloomberg.