He added that he did not consider himself an investor; he plans to offer Citadel his perspective on monetary issues and other matters of public policy that Citadel will use as "inputs" into its investment decisions.
"I was looking for an opportunity to use my skills and knowledge," he said. "This is an interesting firm."
In a statement, Mr. Griffin said: "We are honored to welcome Dr. Bernanke to Citadel. He has extraordinary knowledge of the global economy and his insights on monetary policy and the capital markets will be extremely valuable to our team and to our investors."
Some of Wall Street's richest firms, including private equity and hedge funds, are hiring former central bankers, policy makers and regulators for top positions as they seek to gain an edge in an increasingly competitive and challenging market.
Last year, Timothy F. Geithner, the former Treasury secretary, joined the private equity firm Warburg Pincus. William M. Daley, a former White House chief of staff, joined the Swiss hedge fund Argentière Capital as a managing partner. In 2013, David H. Petraeus, the retired four-star general and former director of the Central Intelligence Agency, joined the private equity firm Kohlberg Kravis Roberts as chairman of its KKR Global Institute.
David H. McCormick, a former under secretary of the Treasury for international affairs in the Bush administration, is now co-president of Bridgewater Associates, the world's largest hedge fund, with $150 billion of assets under management.
"It is inevitable, if you are a bright, knowledgeable, battle-trained regulator or top-level player," said Erik Gordon, a professor at the Ross School of Business of the University of Michigan. "It takes a really unusual public servant to be able to decline the siren song of making a lot of money."
While Mr. Bernanke will remain a full-time fellow at the Brookings Institution, the new role represents his first somewhat regular job in the private sector since stepping down as Fed chairman in January 2014.
His role at Citadel was negotiated by Robert Barnett, the Washington superlawyer who also negotiated a deal for his book, "The Courage to Act," which Mr. Bernanke recently submitted to his editor and will be published in October.
Mr. Bernanke's insights are already much in demand.
At a gathering at the Bellagio Hotel in Las Vegas last May, several hedge fund managers said they had attended dinners with Mr. Bernanke in the first months after he stepped down from the Fed.
"At those dinners he gave credence to the idea that the Fed believed in lower potential G.D.P. and lower potential inflation," Mr. Novogratz told the audience of money managers. For many, that advice was well worth the cost of a seat at the time.
But one hedge fund manager missed out.
"He gave this stuff out," Mr. Tepper said, "but I didn't realize what he was saying at the time, so I didn't do a great trade."