Last year Warren Buffett stunned us all with his incredible gift of $31 billion to the Bill & Melinda Gates Foundation. His generosity will make a huge difference in the lives of people around the world, and his example will be talked about for decades.

But the Warren I know is not just a great philanthropist or businessman. He's also a fantastic teacher. Over the years, Warren has talked to thousands of college students—usually in informal sessions in which his sense of humor and high ethical standards shine through. Warren loves those chats. I think he has more fun swapping ideas with students than he does meeting Wall Street managers. Warren has also been a great mentor to me ever since we met back in 1991. We're both on the board of the Washington Post Co., and in our meetings I've been amazed by the way he can take a problem apart, analyze it and make the solution immediately obvious. One day spent in Warren's company is worth a semester of business school.

Great teachers are also great learners, and Warren is no exception. For instance, although he's famous for being a natural public speaker, it didn't come easily to him. In fact, Warren once told me he used to be terrified of public appearances. So, years ago, he took a class in public speaking. The certificate from Dale Carnegie Training is still hanging on the wall of his office in Omaha, Neb.

That's Warren. He's never afraid to admit what he doesn't know, and he loves to learn. Warren, now 76, has set an example for a whole generation of students, from budding business leaders in Nebraska to a couple of philanthropists in Seattle. We're all lucky to have him.

Gates is co-founder of the Bill & Melinda Gates Foundation, which supports work in more than 100 countries

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