Four years ago, it looked like Timothy Geithner might not survive his confirmation hearings, much less complete a term as Treasury secretary. A background check revealed that he hadn't paid payroll taxes for over two years while working at the International Monetary Fund.

Meanwhile, his chief qualification for the Treasury job was his tour as president of the Federal Reserve Bank of New York, where he executed President George W. Bush's bank bailout.

Geithner leaves office as one of the most important Treasury secretaries in history, having helped rescue the economy from collapse. Clearly there were a few things we misunderstood about him. Here are five of the biggest.

1. Geithner is a creature of Wall Street.

When even the wife of Rahm Emanuel believes you're a Goldman Sachs alumnus, it's going to be tough to convince the country otherwise. But the truth is that before taking over as Treasury secretary in 2009, Geithner spent 20 years in public service, save for a few months at the Council on Foreign Relations.

He worked at Treasury for more than a decade, including a tour as an attache in Tokyo, before joining the IMF and the New York Fed - but he's never worked on Wall Street. His only private-sector experience came at Henry Kissinger's consulting firm right out of grad school. Not surprisingly, Geithner has been defensive about his apocryphal investment-banking past. Appearing at a House Democratic retreat not long after his Senate confirmation in 2009, he blurted out: "I never worked for Goldman. I never worked on Wall Street. I don't come from money."

If there was a problem with Geithner's relationship to the financial sector, it wasn't corruption but intellectual capture. Geithner spent his two decades as a bureaucrat adopting many of the views of the financial-sector elite. When he was New York Fed president, several titans of finance sat on his board of directors. So it came as no surprise when he told me in 2011 that preserving Wall Street's outsize role in the economy was one of the keys to America's strength. "I don't have any enthusiasm for . . . trying to shrink the relative importance of the financial system in our economy," he said.

2. Geithner is mild-mannered and understated.

For years, Geithner's slight frame and boyish looks have inspired doubts about his toughness. Pete Peterson, a financier who once chaired the New York Fed's board of directors, told me that, before he hired Geithner as the bank's president, he "wanted to be sure the soft-spokenness, the diffidence, didn't translate into a lack of courage."

He need not have worried. As Geithner's mentor Larry Summers reassured Peterson, Geithner was "the only person who ever worked with me who'd walk into my office and say to me, 'Larry, on this one, you're full of s---' "

This bluntness was a hallmark of Geithner's tenure at Treasury, at least behind closed doors. When he decided that infighting among regulators could derail Wall Street reform in 2009, he told the heads of the Securities and Exchange Commission, the Federal Deposit Insurance Corp. and the Commodity Futures Trading Commission (CFTC) that their behavior was " 1/8expletive 3/8" ridiculous, advising them to speak with one voice rather than look out for their own turf. In spring 2011, after Standard & Poor's said it planned to downgrade its outlook on the U.S. credit rating, Geithner summoned the company's top officials to Treasury and told them they knew little about how deficit reduction worked in Washington. It's not your "comparative advantage," he told them, according to one participant.

3. He had a relatively free hand in setting economic policy.

Even though Geithner ranks as one of the most influential Treasury secretaries in history, he often didn't get his way on key policy decisions. He was an early opponent of the "Volcker Rule," a proposal from former Fed chairman Paul Volcker to forbid government-backed banks from gambling like hedge funds. But Geithner did an about-face once it became clear that the president was enthusiastic about the idea.

He also pushed back - hard - against then-FDIC Chairman Sheila Bair's plan to create a council of regulators to keep tabs on the country's biggest financial institutions, preferring to leave this task to the Federal Reserve. But Bair, a longtime adversary, maneuvered to make the so-called Financial Stability Oversight Council happen. And because of some unusually public campaigning by CFTC Chairman Gary Gensler, Geithner also had little choice but to accept tougher regulations than he intended for derivatives, the financial instrument that toppled AIG.

4. On taxing and spending, Geithner was a defender of the 1 percent.

To hear liberals tell it, Geithner was a crypto-Republican on fiscal policy: He didn't believe in economic stimulus and was bent on cutting programs such as Medicare to rein in the deficit. The truth is that Geithner supported stimulus in principle and did not dig in against the administration's massive package of tax cuts and spending.

He did support trims to Medicare, but he was the only consistent public voice for ending the upper-income George W. Bush-era tax cuts back in 2010, when Democrats in Congress and the White House largely ducked the fight. In negotiations at the end of that year, he argued that the administration should reject a deal to continue the cuts unless Republicans extended a series of low-income tax credits worth tens of billions of dollars. Republicans reluctantly came around.

5. He leaves behind a financial system that's far safer than before the 2008 collapse.

If you look hard enough, you'll find pieces of Dodd-Frank, the landmark financial reform bill Geithner steered through Congress, that have improved Americans' financial security. But at the broadest level, the law's premise is flawed. Before 2008, massive institutions dominated the U.S. financial system, and the government was overly dependent on outgunned regulators to police them. The results were of course catastrophic. We now have a financial system dominated by even bigger institutions, and the burden of policing them has fallen even more heavily on overmatched regulators.

More than anyone else, this is Geithner's doing. As New York Fed president in 2008, he arranged a series of shotgun marriages between major banks. The following year, Obama made him the intellectual architect of financial reform. The alternative to creating thousands of new rules for regulators to enforce would have been to make the banks smaller and simpler, but Geithner eschewed this approach.

The danger of the new arrangement was on full display last spring, when JPMorgan Chase announced that it had lost $2 billion on a derivatives transaction. (The size of the loss has since grown to roughly $6 billion.) The bank is so large and complex that even its famously fastidious chief executive, Jamie Dimon, had no idea how much risk his traders were taking. After the financial crisis, Geithner believed that you could rein in the banks just by giving regulators more power. JPMorgan proved otherwise.

- - -

Noam Scheiber, a senior editor at the New Republic, is the author of "The Escape Artists: How Obama's Team Fumbled the Recovery."