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In politics, it is called flip-flopping. In banking, it is called postcrisis regrets.

For years, Sanford I. Weill aggressively pushed a “bigger is better” philosophy in banking, turning Citigroup into a financial behemoth through a series of ever-larger deals.

Now, the empire builder wants to break up the banks.

On Wednesday, Mr. Weill called for a wall between a bank’s deposit-taking operations and its risky trading businesses. In other words, he would like to resurrect the regulation that he once fought.

“What we should probably do is go and split up investment banking from banking,” Mr. Weill, the former chief executive of Citigroup, told CNBC. “Have banks do something that’s not going to risk the taxpayer dollars, that’s not going to be too big to fail.”

Since the financial crisis, a number of elder statesmen have pushed to reinstate some form of the Glass-Steagall Act, the 1933 law that separated commercial banks from investment banks.

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In 2009, John S. Reed, who with Mr. Weill forged the megamerger that created Citigroup, apologized for creating a lumbering giant that needed multibillion-dollar bailouts from the government. Philip Purcell, the former chief executive of Morgan Stanley and David H. Komansky, the onetime leader of Merrill Lynch, two other main figures in the fight to repeal Glass-Steagall, have echoed similar concerns about deregulation.

But the comments of Mr. Weill — arguably the most powerful banking voice behind the effort to dismantle Glass-Steagall — have particularly drawn the industry’s attention.

During a Congressional hearing on Wednesday, Representative Carolyn B. Maloney, Democrat of New York, said that Mr. Weill’s remarks appeared to go further than the new rules aimed at curbing banks’ risky activities. Representative Walter B. Jones Jr., Republican of North Carolina, said that one of the worst votes he made in his 18 years in Congress was in favor of bank deregulation.

Richard Drew/Associated Press

In the 1990s, Mr. Weill ushered in the age of the financial supermarket, a model that brought trading, mergers advisory, commercial lending and other disparate banking services under one roof. A serial deal maker, Mr. Weill turned a small bank based in Baltimore into a colossal lender, investment bank and insurer. He capped it with the $70 billion merger between Travelers and Citicorp, which formed Citigroup.

He took pride in his strategy. For years, Mr. Weill had a plaque in his office that listed his accomplishments, including “The Shatterer of Glass-Steagall.”

Glass-Steagall was born out of an earlier crisis, the Great Depression. Enacted in 1933, it was intended to prevent another financial catastrophe by limiting the size and power of the nation’s banks. The new law prompted the breakup of J. P. Morgan & Company, which spun off its brokerage arm to create Morgan Stanley.

With the Depression-era fading from memory, the increasingly powerful banking industry started to chip away at the provisions.

Beginning in the 1960s, regulators started to interpret federal banking rules more loosely, permitting commercial lenders to move into riskier activities like municipal bond underwriting. During his CNBC appearance, Mr. Weill argued that the strictest limits of Glass-Steagall had already eroded by the mid-1980s.

A decade later, he sought to dismiss the last major prohibition for banks, insurance underwriting. The final Senate vote on the Gramm-Leach-Bliley Act of 1999, which formally blessed the universal banking model, was 90 to 8 in favor. The House vote was also lopsided.

His efforts were a major milestone in banking deregulation, paving the way for a new wave of mergers. In 2000, J. P. Morgan united with Chase Manhattan Bank to form JPMorgan Chase. Bank of America embarked on an aggressive deal-making binge.

But critics argued that the deregulation effort would create financial Frankenstein’s monster that could not be effectively run or regulated. They were proved right when the financial crisis brought many banking giants to their knees. After Lehman Brothers collapsed in 2008, Citigroup was forced to take more than $45 billion in bailout money from the government.

Soon after the crisis, some of Mr. Weill’s contemporaries began to reverse their position. In 2010, Mr. Komansky told Bloomberg Television that he regretted helping to lead the charge to cut down Glass-Steagall. Mr. Reed, who briefly shared the top role at Citigroup with Mr. Weill, said that lawmakers were wrong to overturn the law.

Mr. Weill, however, largely kept silent during the debates over financial regulation. Even now, he has refused to say that the banking supermarket model was flawed.

“I think the earlier model was right for that time,” he said on CNBC. “I don’t think it’s right anymore.”

Not all of these banking elders have spoken out of concern for the safety of the global financial system. Both Mr. Weill and Mr. Purcell noted that cleaving apart big banks would improve their stock market values.

But their sentiments are not necessarily shared by their successors. Jamie Dimon, Mr. Weill’s longtime protégé who now runs JPMorgan Chase, turned aside questions about the bank’s size after the latest earnings.

“There’s huge strength in this company that units get from each other,” Mr. Dimon said, who said that splitting up JPMorgan would affect “very short-term stuff.”