(FORTUNE Magazine) – The many surprises in the ranks of the world's billionaires lie not only in who is there, but in who is not. Don't bother to seek out the du Ponts -- none qualify. The name has been synonymous with great wealth in the U.S. for nearly two centuries, but over the years the legacy has splintered. As a group, the du Ponts are certainly billionaires. The family wealth hovers around $10 billion, but some 2,000 trust fund cousins have claims on that pot, giving them an average of $5 million each. That is a comfy nest egg for a Smith or Jones. But a du Pont? Other storied names in U.S. business history, some recalled as malefactors of great wealth, are also absent -- Vanderbilt, Astor, Mellon, Gould, Fisk, Huntington, Crocker, Harriman. No Roosevelt makes the list, nor does a Lehman, a McCormick, a Morse, a Bell, a Carnegie. Perhaps most surprising, the lords of some much publicized real estate empires didn't make the cut. Many billionaires are eager not to be thought rich, but the typical real estate magnate has a vested interest in appearing as wealthy as possible: Easier financing and bigger deals get thrown to the players who are thought to have already made their wad. Donald Trump, 41, is the glamour boy of the business, a self-promoter who has recently been trumpeting his views on public policy in full-page newspaper ads that reek of political ambition. In 1973 he took charge of a solid but unspectacular family firm, founded by his father and centered on working-class apartment houses in New York City's prosaic outer boroughs of Queens and Brooklyn. Donald turned it into a flashy business that controls such wonders as Manhattan's 68-floor Trump Tower, where apartments sell for an average of $5 million each. Making deals is what Trump is all about. He is a syndicator, pushing leverage to the tipping point, trading on image more than reality. What Trump is not is a billionaire. Published estimates of his net worth run as high as $3 billion, a number that might be in the ballpark if he got top dollar for each of his properties and if his proposed 78-acre TV City project on Manhattan's West Side ever moves off the drawing boards. But strike the fast talk and hyperbole, and Trump cashes in at below a billion. Trammell Crow, 73, is another familiar name missing from the list. Head of a recently diminishing Texas-based real estate empire, Crow has hiked the Himalayas. But he has yet to scale the heights of phenomenal wealth. In true ten-gallon style, he says that he, his wife, Margaret, and their six children have a net worth of $1 billion. Some real estate experts think he's twirling his lariat. Says one disbeliever: ''Trammell Crow has overappraised his own worth just like he overappraises his own handsomeness.'' Declining oil prices and a collapse of real estate values account for other notable absences from the list: some scions of H. L. Hunt, the billionaire oilman. Margaret Hunt Hill, Harold ''Hassie'' Hunt III, and Ray Hunt have managed to keep their inheritances in the billion-dollar league. But Bunker, Herbert, and Lamar have not; Placid Oil and other major holdings are in Chapter 11. Their quiet sister, Caroline Rose Hunt, 64, who recently resumed her maiden name after her divorce from Hugo W. Schoellkopf Jr., also falls short of a billion, but not by much. She has some $950 million, including luxury hotels like the Mansion on Turtle Creek in Dallas and the Bel-Air in Los Angeles. Readers of the financial pages will look in vain for Australian raider Robert Holmes a Court. Among famous non-Americans who look like billionaires in the gossip columns but are not by FORTUNE's accounting are Monaco's Prince Rainier and Saudi Arabian Adnan Khashoggi, a sometime businessman, arms dealer, and middleman whose name figured in the recent Iran-contra caper. Prince Rainier, 64, may rule Monaco, the handkerchief-size jet-setters' playground, but in terms of wealth he's more a maitre d' than the equal of some of the players drawn to the Monte Carlo casino. Despite his regal status, lifestyle, and marriage to the late Hollywood Princess Grace Kelly, Rainier's net worth is only about $500 million. Khashoggi, 52, who has taken the high life to the ionosphere, has been beset by financial difficulties. Once called the richest man in the world, he probably never was -- which hardly matters because, explains a Khashoggi aide, ''It's not how much he has, but how much he spends.'' The aide adds, ''Anyone can make a billion dollars, but how many people know how to spend it?'' It's a question worth pondering.