The friendship between Warren E. Buffett and Bill Gates has been forged over a shared passion for such homespun American treats as cherry Coke, burgers and college football. They delight as well in loftier pursuits, like playing bridge and solving complex math problems.

But, more than anything, what Buffett's $31 billion gift to the foundation that Gates runs with his wife, Melinda, shows is a common disdain for inherited wealth and a shared view that the capitalist system that has enriched them so handsomely is not capable alone of addressing the root causes of poverty.

"A market system has not worked in terms of poor people," Buffett said this week, in an interview taped earlier in the day for "The Charlie Rose Show" on PBS.

As for any thought he might have had in giving the bulk of his billions to his three children, Buffett was characteristically blunt. "I don't believe in dynastic wealth," he said, calling those who grow up in wealthy circumstances "members of the lucky sperm club."

Genuine friendships within the highest tier of corporate America are rare, because of the demands of the jobs as well as the myriad forces that can turn shared interests into embarrassing conflicts.

But the bond between Buffett and Gates, the two richest people in the United States and arguably the two most influential in American business in recent years, has lasted more than 15 years. It has been sustained, according to people who know them, in large part by a very high level of intelligence and a conviction that their vast wealth has given them a larger responsibility to society.

"When you are as smart as Warren or Bill, I think it's hard to find people to talk to," said Donald E. Graham, the publisher of The Washington Post, who has spent time together with the two men. He called Buffett's gift "the most creative thing that anyone has done and the way he has done it underscores how much admiration he has for Bill."

What was most surprising about Buffett's decision was not so much that he was giving his wealth away but that he was asking someone else to pursue philanthropy on his behalf.

Like Buffett, corporate titans like Sanford I. Weill, the former chief executive of Citigroup, and Henry M. Paulson Jr., the chief executive of Goldman Sachs who has been nominated to be Treasury secretary, have promised to dispense with their own wealth. But they, like most of those with huge fortunes, are expected to set up their own charitable foundations to carry out their wishes. For Buffett, a hallmark of his skill as an investor has been his self-denying quality. He has often described his task running Berkshire Hathaway, the insurance holding company that serves as his investment vehicle, as finding the best corporate managers, investing heavily in them and getting out of the way--an approach that he now plans to follow with the Gateses.

"I would be terrible at it," Buffett said this week, assessing his abilities as a philanthropist. "I like to look in the mirror and ask myself whether I'm doing OK. And there are a lot of people whose opinions I don't want to listen to. So you have to be a little more diplomatic than I am."

In past interviews, Gates, who just turned 50 and is 25 years younger than Buffett, has referred to himself as the student in the relationship ("I study him," he has said).

But while business itself has not been at the core of their relationship, Buffett invited Gates to serve as a director of Berkshire Hathaway and said that he had bought a small piece of Microsoft a long time ago just to keep his eye on Gates.