David Rubenstein grew up in modest home in Baltimore, the son of a post-office worker who made $7,000 a year. Neither of his parents finished high school or graduated college. But this, he told an audience at the Washington Ideas Forum Wednesday, was his great advantage, because "when you realize you have to do something on your own, you work harder."

Rubenstein is known both for his financial acumen and for his philanthropy—he, like Bill Gates, and Warren Buffett, has signed the Giving Pledge, and aims to give away almost all of his $3.1 billion fortune before he dies. But his success in the private equity world only came after a period spent as a lawyer and a stint working in public policy for the Carter administration, where, he said, "I managed to get inflation to 19 percent and the country didn't want me to stay." After feeling that he wasn't particularly gifted in either of those fields, he started the Carlyle Group, then the first buyout firm in Washington, and now one of the largest private equity firms in the world. This success finally gave Rubenstein the opportunity to do what he'd always hoped to—to give back to the nation that he credits for enabling his success. "I don't think I could have done this in other countries," he said.

Rubenstein's philanthropy extends to many of Washington's most revered institutions, from the Washington Monument (where, he said, he scribbled his initials on a private tour after he helped fund repairs to the shuttered memorial) to the National Archives, which currently displays the copy of the Magna Carta that Rubenstein purchased for $21.3 million in 2007. It was important to him, he said, to keep the document in the United States because of the role it played in inspiring the Constitution and the Bill of Rights.

Rubenstein also donated $4.5 million to the National Zoo's panda program after realizing that there were only around 1500 giant pandas left in the world compared to 7 billion humans. He compared the animals to politicians in analyzing how bad they are at reproducing. "Members of Congress," he said, "know what they're supposed to do but they don't know how to do it. The pandas are the same way."

After purchasing the Magna Carta—the only one of 17 existing copies in the world to be in private hands—from Ross Perot at Sotheby's, Rubenstein recalled how he told reporters that he wanted to give it to "the United States as a downpayment for my obligation to repay the country for everything I've had." This, he said, is how he defines his principle of patriotic philanthropy, and his ongoing attempt to "recognize the unique rights and freedoms we have this country."