“It is obscene for so much wealth to be held in the hands of so few when one in 10 people survive on less than $2 a day,” Winnie Byanyima, executive director of Oxfam, said in a statement. “Inequality is trapping hundreds of millions in poverty. It is fracturing our societies and undermining democracy.”

Yet the anger against the superrich has abated since the Occupy Wall Street protests in 2011. Protesters seem to be more concerned with the actions of Mr. Trump (who is likely a billionaire, although he has provided little proof of his real wealth) than with his cabinet of plutocrats.

One of his tax proposals would keep billionaires from having to part with more of their wealth, by eliminating the estate tax. Without it, generational wealth would be easier to preserve and perpetuate.

Philanthropy has become important to many billionaires, and not just through the Giving Pledge, Mr. Buffett’s compact to get the wealthiest to give away at least half of their fortunes. Nor is it confined to the United States, with its tradition of charitable giving.

“You’re starting to see where philanthropy is becoming more and more important to billionaires regardless of where they live,” Mr. Mathews said. “I don’t know if 10, 12 years ago, it was much of a conversation in Asia. Now all billionaires, regardless of where they live, are worried about the next generation.”

But there are limits to what even a billionaire can do. Mr. Bloomberg, in an interview in 2014, recalled the time he was approached at a conference in Sun Valley, Idaho, by a hedge fund manager offering him $1 billion over five years to change public education in New York.

“When I explained to him that New York City’s annual school budget was $22 billion a year,” Mr. Bloomberg said, “that was the last time we ever heard from him.”