Bill Gates Urges Obama to Increase Spending

The foundation is akin to a start-up. "It's like a large company with a big vision and a determination to grow rapidly," said Duke University professor Joel L. Fleishman, who studies philanthropy. "But in this case, it's not growing to make money. It's growing to figure out how to give away money in an orderly and effective fashion."

Philanthropic leaders have looked upon the foundation's rise with awe. "It's the largest in the world by a factor of two, and that's astonishing," said Harvey P. Dale, a nonprofit law professor at New York University. But, he said, some leaders "are jealous of it, some feel threatened by it, including some of the foundations who were hugely dominant and now, by comparison, are relatively modest."

But many other philanthropists try to emulate Gates. "When you're as large as Gates, the market moves when you move," said Larry Brilliant, a health expert who directs Google's giving.

"Great public health accomplishments on a global scale require prescience. They require resources. They require scientific and managerial excellence, and maybe most importantly, they require leadership and public will," Brilliant said. "This is something only Gates can do."

It is too soon to determine whether Gates's work will have a lasting impact, experts said.

"The jury is definitely still out," said Fleishman, who has written a history of foundations. "They're going about things in the right way, but it is still too early to say that they have had an unqualified success. . . . The problems are just so big."

Asked what his legacy may be in 15 years, Gates said he hopes it would be as a catalyst for "dramatic improvement in global health. . . . I expect that we would have played a role in a dramatic reduction in disease in many of the top areas: malaria, tuberculosis, AIDS, childhood diseases."