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 Mr. Buffett and Mr. 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 Mr. 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 Mr. 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.

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Like Mr. 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 Mr. 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 Mr. and Ms. Gates.