"I knew from that day on that I wanted to go into public service and work in the White House," he says.
So three years after graduating from law school, he signed on as legal counsel to Sen. Birch Bayh of Indiana, who was contemplating running for the Democratic presidential nomination. After Bayh dropped out of the race, Rubenstein joined the campaign to elect a Georgia peanut farmer named Jimmy Carter.
"When I came on board, Jimmy was 33 points ahead in the race," Rubenstein says. "By the election, he was ahead by just 1 point. So you can see how effective I was."
The young staffer quickly distinguished himself by a self-discipline that bordered on the monastic, sleeping in his office and subsisting on yogurt and crackers from vending machines.
Today, he exhibits a willingness to sacrifice personal pleasure for a larger goal. A vegetarian, Rubenstein doesn't drink alcohol or smoke.
He famously has no hobbies When he does indulge in a seemingly frivolous pursuit, such as attending a sporting event, his approach is characteristically information-based. According to Levy of the Lincoln Center, Rubenstein has memorized vast amounts of arcane baseball statistics.
Even the speed-reading can be seen as evidence of a tendency toward the ascetic. In order to cover a large amount of literary ground in a small amount of time, Rubenstein is willing to forgo the delights to be gained by lingering over individual words, sentences and ideas.
"If I sit on a beach, I'm afraid that at that moment, my immune system will relax and germs will come in, and I'll get a disease that will kill me," he says, the corners of his mouth tilting upward at his own joke. "If you love what you do, if your mind is actively engaged, it's not work."
In 1981, after Carter lost his bid for re-election, Rubenstein went back to practicing law, but quickly became bored. He began casting about for a new challenge with two friends, William E. Conway Jr. and Daniel A. D'Aniello.
The three decided to create an international private equity firm based in Washington and outside New York's financial power corridor. They named their company after the hotel in the Big Apple where the trio initially concocted their plan.
The Carlyle Group's rise was meteoric. The firm was created in 1987 on an initial investment of $5 million. Today, it has $90 billion in assets and offices in 19 countries. Rubenstein ranks 123rd on Forbes magazine's 2009 list of the 400 wealthiest Americans, with an estimated net worth of $2.5 billion.
But with success has come some controversy.
Carlyle was excoriated in Michael Moore's 2004 film "Fahrenheit 9/11," which made much of a $2 million investment in the company by Osama bin Laden's estranged half-brother. After the connection was made public, that money was returned.
In addition, the prominent political figures who served as Carlyle board members and advisers — including former President George H.W. Bush, former British Prime Minister John Major and former Secretary of State James Baker III — led some critics to insinuate that the firm was manipulating the government for personal gain. The Carlyle Group is widely thought to have been the model for the sinister Manchurian Global Corp. in Jonathan Demme's 2004 remake of "The Manchurian Candidate."
At the time, Rubenstein maintained that his company had never engaged in questionable business practices. And it's been several years since the firm has shed the high-profile pols that once raised so many eyebrows.
"Balzac said that behind every great fortune, there is a great crime," Rubenstein says. "Some people think that if you have made a great deal of money, you must have done something wrong. But that is behind us now. I haven't thought about it in years."
Levy of the Lincoln Center researched the controversy before inviting Rubenstein to sit on that organization's board, and he concluded that there was no basis to the innuendos.
"I did my homework about Carlyle, and so did the other members of the board," he said. "I had no hesitation whatsoever about asking David to join us. None. He is very disarming and totally honest. If you're curious about something, just ask him."
In a way, Rubenstein identifies with the skeptics.
"I ask myself, 'How did I get so lucky?' " he says.
He is determined to share his wealth with those who are less fortunate, though at the moment he's struggling with the most effective way to accomplish that goal.
He won't say how much money he and his wife have given away, but suffice to say, it's an impressive sum: There's $5 million to the National Book Festival, $3.5 million to the Kennedy Center, $5 million to the Johns Hopkins Children's Center, and so on.
Oddly enough, the wide-ranging nature of his generosity is causing him some concern.