Turner channeled his money through the United Nations Foundation, where it was leveraged to get other contributions so as to bring $2 billion to finance causes from malaria to polio, from climate change to family planning.

The gift brought new respect to the United Nations and made it increasingly fashionable for billionaires to worry about global poverty. These tycoons bring not just their checkbooks to the table but also a business sensibility that introduces greater rigor and evaluation to the world of bleeding hearts.

All this has helped shine a greater spotlight on neglected issues — which, in turn, has led to extraordinary results. A study this month reported that infant mortality around the world dropped by more than half from 1990 to 2010. That’s millions of lives saved each year.

Of course, not everybody has gotten the memo. Take Donald Trump, who has contributed his name to a foundation but little more. An investigation by The Smoking Gun Web site described him as possibly “the least charitable billionaire in the United States,” for he apparently gave the foundation just $3.7 million — over 20 years. Trump, who has said he is worth $7 billion, is not even the largest contributor to his own foundation.

(A spokesman for Trump suggested that it would be “totally incorrect” to characterize him as uncharitable, saying that he has also donated land in upstate New York for public parks and “millions of dollars” to other causes.)

Turner isn’t shy about encouraging others to jump on board. When I asked if he had any advice for my readers, he grew particularly animated: “You don’t have to have any money to make a difference; you can pick up trash walking down the street, and I do that all the time,” he said. “You can volunteer your time. You can be a big brother or a big sister.”