By some argument, using a┬ápercentage of GNP, John D. Rockefeller, the oil monopolist who died in 1937, was the richest man in American history; his net worth at its peak was some 2 percent of America’s annual income. Andrew Carnegie, the philanthropic steelmaker who died in 1919, may have been the second wealthiest American, with a similar slice of the GNP.

Bill Gates’ net worth amounts to less than 1 percent of the current national income. An economy that has grown into the trillions of dollars makes it less likely that any individual can own a substantial part of it. That fact alone means Bill Gates will probably never enjoy the political power that Rockefeller and Carnegie wielded at the peaks of their careers.

A third way to compare wealth across time is to look at the ratio between the earnings of the richest people and the earnings of the average citizen. By that calculation, the gap between Bill Gates and the Main Street man or woman is wider than at any time in history. In fact, calculations performed in 2007 suggest that for Bill Gates, $350,000 spent to buy a Lamborghini, for instance, would be the equivalent for the average American to spending 73 cents.

But whether the gap was greater or less for Mahmud or Genghis Khan and their subjects is impossible to say. How does one count elephants or kingfisher feathers in such a calculation? How can income or buying power be measured in moneyless societies?

In 2009, Bill Gates’ net worth passed the $200 billion mark. Even with the nearly infinite number of ways a person can spend money in the twentieth century, Bill Gates is hitting the limits of modern consumption – he can’t get rid of his money as fast as it comes in. He built a 45,000-square-foot mansion near Seattle that is filled with technological wonders – the master bathtub, for example, can be programmed to fill to the right temperature and depth by Gates from his car. He takes vacations on a private railroad train.

He owns his own jet and a fleet of sports cars. What does Bill Gates want that he doesn’t have? It’s difficult to imagine what the Gates fortune will buy in one hundred years that it can’t buy right now – a city? An ocean? The moon? “In an economy, such as that of the United States of America, where leisure is barely moral,” wrote the economist Wilfred Beckerman, “the problem of creating sufficient wants – to absorb productive capacity may become chronic in the not-too-distant future.”

More proof of Bill Gates’ status as the cultural hero of late twentieth-century America is that the country’s working class doesn’t seem to hate him as they did so many earlier multimillionaires.

That may be explained by their own standard of living, which, though not constantly rising, greatly exceeds that of their immigrant great-grandparents, who lived in tenements, worked six-day weeks, and buried many of their own children. Earlier millionaires worried about labor upheavals or even a working-class revolution with good reason. Bill Gates, by contrast, is much beloved on his corporate campus near Seattle and ferociously defended by purveyors and adherents of the American dream.